Large-signal modeling and simulation of switching DC-DC converters

A general nonlinear continuous formulation procedure for large-signal analysis of switching DC-DC converters is presented. The method can be applied in either of the two conduction modes, and it is easily programmed for computer-aided analysis with small simulation time. A boost regulator operating in constant-frequency current-programmed mode is used to illustrate the application of the method. A stability graph is subsequently developed to facilitate the design of DC-DC switching regulators for large-signal applications. The graph provides an estimation of the values of input voltage and load resistance leading to a stable regulator behavior     

Current Variability in Si Nanowire MOSFETs Due to Random Dopants in the Source/Drain Regions: A Fully 3-D NEGF Simulation Study

In this paper, we study the impact of random discrete dopants in the source/drain (S/D) leads on the current variability of a gate-all-around Si nanowire transistor. Due to the strong inhomogeneities of the self-consistent electrostatic potential, a fully 3D real-space nonequilibrium Green's function (NEGF) formalism is used. N-channel transistors with random discrete donors in the S/D regions varying in both numbers and locations have been simulated. We have studied the impact of quasi-bound (QB) states and transmission resonances associated with the attractive potential of the donors on the screening of the impurities and on the current transport. The convergence of the coupled 3D Poisson-NEGF equations for narrow wires with discrete dopants is cumbersome due to the quasi-discrete nature of QB states and resonances of the attractive impurity potential. We present a robust solution strategy dealing with the convergence challenges. Large variations in the on-current and modest variations in the subthreshold slope are observed in the I _D-V _G characteristics when comparing devices with microscopically different discrete dopant configurations. We have also estimated the access resistance associated with the random dopant regions in the source and the drain leads and find very good agreement with the resistance estimated from the bulk silicon mobility at the same doping concentration.     

Optoelectronic study in porous silicon thin films

A photoconductivity (PC) study in as deposited porous silicon (PS) thin films is presented in this work. PS thin films were produced by the electrochemical anodizing method at different anodizing times. The films surfaces were characterized by SEM and porosity was determined by gravimetric methods. Photoluminescence and PC measurements were taken at room temperature. The maximum of the photoluminescence spectra are located around 650 nm, whereas those of PC are placed around 400 nm. The maximum of the photoluminescence signal shifts toward short wavelengths as the quantum dimension of the material skeleton diminishes, while any spectral displacement of the photocurrent signal as the porosity of the material increases is not observed. The spectral position of the PC signal does not change because it is strongly affected by the large quantity of defects present in the sample surface which diminishes the mean free path of the carriers to reach the electrodes. In all the samples photocurrent is small around 10^?1 μA and the intensity of the signal goes down as the porosity increases. Two mechanisms exist that compete with one another, the carrier generation and recombination through light emission centers which diminish the photocurrent.     

Dynamic Policy-Based Network Management for a Secure Coalition Environment

This article reports the latest results of an R&D effort to develop a prototype implementation of a dynamic policy-based network management (PBNM) system that can be used to configure and manage a secure network for a coalition environment across an unsecured wide area network. The prototype, based on a distributed architecture, includes capabilities for policy creation and management, dynamic policy negotiation, and dynamic policy provisioning. The policy negotiation facilitates the rapid deployment of a coalition network while the dynamic policy provisioning automates the configuration and management of network services including firewalls, virtual private network connections, routing, quality of service (QoS), and domain name services. Such a PBNM system enhances an organization's ability to react to network incidents identified by a network situational awareness assessment. Although the focus of the current research is a military coalition environment, the system can be used in any distributed enterprise or collaborative environment     

High extinction ratio and high-temperature 2.5-Gb/s floor-free 1.3-/spl mu/m transmission with a directly modulated quantum dot laser

For the first time with a directly modulated InAs-GaAs quantum-dot laser, high extinction ratio (up to 17 dB) and 25/spl deg/C-85/spl deg/C single-mode-fiber data floor-free transmissions are achieved at 2.5 Gb/s. Moreover, an interferometric technique showed a nearly constant Henry factor /spl sim/2 until a bias current six times the threshold current.     

Improved thermal analysis of buried landmines

In this paper, we address the problem of the detection and identification of surface-laid and shallowly buried landmines from measured infrared images. A three-dimensional thermal model has been developed to study the effect of the presence of landmines in the thermal signature of the bare soil. Based on this model, a target identification procedure is proposed aiming at detecting and classifying the anomalies found on the soil thermal signature. In our approach, landmines are thought of as a thermal barrier in the natural flow of the heat inside the soil, which produces a perturbation of the expected thermal pattern on the surface. The detection of these perturbations will put into evidence the presence of potential mine targets. We propose an iterative procedure to classify the detected perturbations as mines or nonmines and to estimate their depth of burial. This paper describes the main principles of our method and illustrates classification results on a set of acquired images. Qualitative and quantitative comparisons with independent component analysis are also given.     

Dimensionality reduction and classification of hyperspectral image data using sequences of extended morphological transformations

This work describes sequences of extended morphological transformations for filtering and classification of high-dimensional remotely sensed hyperspectral datasets. The proposed approaches are based on the generalization of concepts from mathematical morphology theory to multichannel imagery. A new vector organization scheme is described, and fundamental morphological vector operations are defined by extension. Extended morphological transformations, characterized by simultaneously considering the spatial and spectral information contained in hyperspectral datasets, are applied to agricultural and urban classification problems where efficacy in discriminating between subtly different ground covers is required. The methods are tested using real hyperspectral imagery collected by the National Aeronautics and Space Administration Jet Propulsion Laboratory Airborne Visible-Infrared Imaging Spectrometer and the German Aerospace Agency Digital Airborne Imaging Spectrometer (DAIS 7915). Experimental results reveal that, by designing morphological filtering methods that take into account the complementary nature of spatial and spectral information in a simultaneous manner, it is possible to alleviate the problems related to each of them when taken separately.     

Microwave photonic transversal filter for intermodal dispersion equalisation

An experimental demonstration is given of the use of a transversal RF photonic filter to accomplish intermodal dispersion equalisation in a 10 Gbit/s optical fibre link using a Fabry-Perot laser. The structure operates in an equivalent fashion to an electronic equaliser but in the photonic domain. A record distance of 24.2 km using the equalising filter is obtained.     

Floor free 10-Gb/s transmission with directly modulated GaInNAs-GaAs 1.35-/spl mu/m laser for metropolitan applications

Among the new semiconductor materials for telecom devices, the GaInNAs-GaAs structure presents interesting properties for low-cost applications, like high differential gain and high T/sub 0/. Another key aspect of the performance is the behavior of the GaInNAs-GaAs based lasers under high bit rate direct modulation. Here, we demonstrate the dynamic capabilities of GaInNAs-GaAs three-quantum-well ridge structure through 2.5-Gb/s directly modulated laser emission and transmission on standard fiber, in the temperature range 25/spl deg/C-85/spl deg/C. Besides transmission is demonstrated up to 10 Gb/s at 25/spl deg/C on the same fiber, without penalty and bit-error-rate floor.