Spectral Properties of Active Racetrack Semiconductor Structures With Intracavity Reflections

The effects of intracavity reflections in active racetrack semiconductor resonator structures are studied. The incorporation of active material facilitates probing into effects stemming from even minute reflections, such as mode mismatching, which are almost undetectable in passive structures. The spectral response of these structures are studied by the transfer matrix method that models the racetrack resonator as a multicavity structure formed by the various optical paths induced by intracavity reflections. The signature of the structural and operational parameters on the spectral response enables the identification of the conditions for the appearance of interesting spectral properties such as mode splitting and Fano resonances.     

Theoretical study of GaInNAs-GaAs-based semiconductor optical amplifiers

We have calculated the basic properties of multiple-quantum-well semiconductor optical amplifiers (SOAs) with active regions based on the newly proposed material GaInNAs. The band structure is modeled using k/spl middot/p theory and accounting for strain effects and the material gain in the context of free-carrier theory. The performance of structures with different nitrogen composition that emit at the same wavelength is modeled using a multisection approach accounting for spontaneous emission. The trends in the SOA performance related parameters are identified and explained.     

Proposed scheme for polarization insensitive GaInNAs-based semiconductor optical amplifiers

A novel scheme for polarization insensitive GaInNAs-based semiconductor optical amplifiers is proposed in which TE and TM polarization gain is almost equal for GaInNAs quantum wells with GaInAs barriers. The proposed scheme involves the growth of GaInAs metamorphic layers on GaAs. Based on a k /spl middot/ p Hamiltonian that accounts for the N-induced modifications of the bandstructure, we calculate the optical properties of GaInNAs-GaInAs quantum wells and explore the effect of GaInAs barriers on the valence band mixing effects. The TE and TM amplifier gain of GaInNAs-based semiconductor optical amplifiers with GaInAs barriers is then analyzed.     

Template-guided inspection of arbitrarily oriented targets

The performance of template-based inspection of randomly oriented targets relies on the effective operation of two procedures: image registration and change detection. Each procedure is characterised by its own challenges. Real-time applications require that image registration is performed in an acceptable time with accurate results, regardless of structural distortions. Change detection can be hindered by noise fluctuations and illumination variations. An additional challenge in template-guided change detection comes from the fact that the decision needs to be based on a comparison restricted to two frames. The operation principles of a template-guided change detector are analysed. Image registration is based on a wavelet-based method which employs mutual information. A block-based change detection algorithm, which separates content alterations from noise-level fluctuations, illumination variations and shadows, is also analysed. The principles presented are combined for the implementation of a sample template-guided undervehicle surveillance system. The architecture of the system and its experimental results are presented, and practical aspects and considerations regarding the system design are discussed.     

Concatenation performance of optical packet switches that incorporate wavelength converters based on four-wave mixing in semiconductor optical amplifiers

Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) has been acknowledged as a useful wavelength conversion technique especially due to its ability to convert sequences of ultra fast pulses but also simultaneously a number of wavelengths. An analysis is used to investigate the concatenation performance of optical packet switch that incorporate wavelength or waveband converters based on FWM in SOAs.     

A reconfigurable iterative algorithm for the K-user MIMO interference channel

Interference alignment (IA) is a recently proposed transmission technique for the K  -user interference channel (IFC), which is proven to achieve a sum-rate multiplexing gain of K/2$K/2$ at the high interference regime. Motivated by our recent work [1] that showed how the sum-rate scaling can range between K/2$K/2$ and K for moderate-to-low interference conditions, in this paper we present a novel iterative algorithm for the K-user multiple-input multiple-output (MIMO) IFC with arbitrary number of transceiver antennas. The proposed algorithm automatically adjusts itself to the interference regime at hand, in the above sense, as well as to the wireless channel in order to achieve the appropriate sum-rate scaling. Our reconfigurable algorithm combines the system-wide mean squared error minimization criterion with the single-user waterfilling solution to maximize each user's transmission rate according to the interference levels and channel conditions. Extensive computer simulation results for the sum-rate performance of the proposed reconfigurable algorithm over various Ricean fading channels are presented. It is shown that, in the interference-limited regime, the proposed algorithm reconfigures itself so as to achieve the IA scaling whereas, in the moderate-to-low interference regime, it chooses interference-myopic MIMO transmissions for all K communication pairs.     

Polygonal plate modeling of realistic structures

A technique for the electromagnetic modeling of arbitrary perfectly conducting structures using polygonal plates is described. The method is illustrated by three realistic examples.     

Medullary Thymic Epithelial Cells and Central Tolerance in Autoimmune Hepatitis Development: Novel Perspective from a New Mouse Model

Autoimmune hepatitis (AIH) is an immune-mediated disorder that affects the liver parenchyma. Diagnosis usually occurs at the later stages of the disease, complicating efforts towards understanding the causes of disease development. While animal models are useful for studying the etiology of autoimmune disorders, most of the existing animal models of AIH do not recapitulate the chronic course of the human condition. In addition, approaches to mimic AIH-associated liver inflammation have instead led to liver tolerance, consistent with the high tolerogenic capacity of the liver. Recently, we described a new mouse model that exhibited spontaneous and chronic liver inflammation that recapitulated the known histopathological and immunological parameters of AIH. The approach involved liver-extrinsic genetic engineering that interfered with the induction of T-cell tolerance in the thymus, the very process thought to inhibit AIH induction by liver-specific expression of exogenous antigens. The mutation led to depletion of specialized thymic epithelial cells that present self-antigens and eliminate autoreactive T-cells before they exit the thymus. Based on our findings, which are summarized below, we believe that this mouse model represents a relevant experimental tool towards elucidating the cellular and molecular aspects of AIH development and developing novel therapeutic strategies for treating this disease.