F. De Paola

Flood risk assessment for informal settlements

The urban informal settlements are particularly vulnerable to flooding events, due to both their generally poor quality of construction and high population density. An integrated approach to the analysis of flooding risk of informal settlements should take into account, and propagate, the many sources of uncertainty affecting the problem, ranging from the characterization of rainfall curve and flooding hazard to the characterization of the vulnerability of the portfolio of buildings. This paper proposes a probabilistic and modular approach for calculating the flooding risk in terms of the mean annual frequency of exceeding a specific limit state for each building within the informal settlement and the expected number of people affected (if the area is not evacuated). The flooding risk in this approach is calculated by the convolution of flooding hazard and flooding fragility for a specified limit state for each structure within the portfolio of buildings. This is achieved by employing the flooding height as an intermediate variable bridging over the fragility and hazard calculations. The focus of this paper is on an ultimate limit state where the life of slum dwellers is endangered by flooding. The fragility is calculated by using a logic tree procedure where several possible combinations of building features/construction details, and their eventual outcome in terms of the necessity to perform structural analysis or the application of nominal threshold flood heights, are taken into account. The logic tree branch probabilities are characterized based on both the orthophoto recognition and the sample in situ building survey. The application of the methodology is presented for Suna, a sub-ward of Dar es Salaam City (Tanzania) in the Msimbazi River basin having a high concentration of informal settlements.

Surface-passivated high-resistivity silicon as a true microwave substrate

This paper addresses the properties of a surface-passivated (enhanced) high-resistivity silicon (HRS) substrate for use in monolithic microwave technology. The detrimental effects of conductive surface channels and their variations across the wafer related to the local oxide and silicon/silicon-dioxide interface quality are eliminated through the formation of a thin amorphous layer at the wafer surface. Without passivation, it is found that the surface channels greatly degrade the quality of passive components in HRS by masking the excellent properties of the bulk HRS substrate and by causing a spread in parameters and peak values across the wafer. Moreover, it is seen that the surface passivation leads to excellent agreement of the characteristics of fabricated components and circuits with those predicted by electromagnetic (EM) simulation based on the bulk HRS properties. This is experimentally verified for lumped (inductors and transformers) and distributed (coplanar waveguide, Marchand balun) passive microwave components, as well as for a traveling-wave amplifier, through which also the integration of transistors on HRS and the overall parameter control at circuit level are demonstrated. The results in this paper indicate the economically important possibility to transfer microwave circuit designs based on EM simulations directly to the HRS fabrication process, thus avoiding costly redesigns.

A scalable physical model for coplanar waveguide transition in flip-chip applications

In this paper we present a new scalable electrical lumped model for coplanar waveguide (CPW) transitions in flip-chip modules. The model is developed by a proper reduction of the well-known electrical model of two coupled coplanar waveguides. Electromagnetic simulations of the structure are used to extract model parameters for various bump configurations. Regression models are then used in order to scale the values of the lumped elements with physical dimensions of the system. The good agreement between fast circuit simulations and time-consuming finite element analysis, indicate that the model is well suited for modeling flip-chip CPW in the high-GHz range.

Fully Automated Electrothermal Simulation Using Standard CAD Tools

This contribution presents a novel simulation tool for the electrothermal analysis of solid-state devices and circuits in both static and transient conditions. The code relies on an effective analytical approach to describe the 3D thermal process, and exploits the engine of the commercial software ADS (Advanced Design System) to consistently solve the electrical and thermal networks. Features like model accuracy, lack of convergence problems, low time/memory requirements, flexibility and user friendliness make the proposed software a good alternative to SPICE-like and fully numerical tools for the optimization of both reliability and performance of state-of-the-art devices/circuits

Trade-offs in RF Performance and Electrothermal Ruggedness of Multifinger SiGe Power Cells

In this contribution we analyze the trade-offs existing between the RF performances and the thermal ruggedness of SiGe power multifinger HBTs. Six structures with constant emitter area and different emitter geometry are considered. Small signal S-parameters as well as large signal load-pull measurements are performed to evaluate the effect of emitter geometry on the device RF performances. Moreover, the structures are analyzed through an in house developed electrothermal simulator in order to define the layout influence on the safe operating area (SOA). Finally, some guidelines are drawn to help the designer in trading electrical performances for thermal ruggedness

Enhancing Commercial CAD Tools toward the Electrothermal Simulation of Power Transistors

In this contribution, we present a novel simulation strategy for the electrothermal analysis of power multicellular transistors. The approach is based on the enhancement of a commercially available circuit simulator, namely Agilent advanced design system, and relies on an effective approach to describe the 3-D thermal process in both steady-state and transient conditions. A prototype of vertical power bipolar transistor has been considered as a case-study. The fairly good agreement between simulated and experimental results demonstrates that the proposed methodology can be successfully exploited for forecasting the electrothermal behavior of power transistors with complex layout, thus providing plain guidelines to improve their thermal ruggedness

Probabilistic Assessment of Debris Flow Peak Discharge by Monte Carlo Simulation

AbstractThe topographic and hydrologic parameters involved in the estimation of the debris flow peak discharge in a classical approach are usually assumed to be deterministic. As a result, in such approaches, the only uncertainty in the evaluation of peak discharge is the evaluation of rainfall intensity and frequency. The present study aims to provide a probabilistic approach for estimating the debris flow peak discharge through the use of a Monte Carlo simulation method. Studies on such landslides in pyroclastic deposits have been performed in order to identify potential source areas and the main depositional mechanisms. The standard Monte Carlo simulation is used in order to propagate the uncertainties in different paramaters, related to hydrographic basin modeling, and to obtain a probability distribution for the peak discharge, related to a given return period. As a numerical example, the peak discharge of debris flow in the basin of the Corbara Stream, located in the municipality of Salerno in south...

A Semi-Probabilistic GIS-Based Method for Meso-Scale Flood Hazard Zonation

Identification of the flood-prone areas can be considered as a fundamental step in a flood risk management procedure. This work focuses on a fast procedure for hazard zoning within the flood-prone areas at a meso-scale. To this end, a semiprobabilistic GIS-based methodology for hazard zoning of the potentially flood-prone areas is presented. The main output consists of GIS-compatible maps for the hazard zoning (by flood height) of the potentially flood-prone areas. A flood heightdependent extension of the topographic wetness index (TWI) threshold is proposed as the lower-limit TWI for zones with flood height larger than a prescribed value. This procedure relies on calibrating the flood height-dependent topographic wetness index (TWI) threshold through maximum likelihood estimation and based on the inundation profiles calculated at micro-scale level for a given spatial window. This calibration is performed for different values of flood depth in order to investigate the correlation between the TWI threshold and the flood depth conditioned on return period, through simple linear regression. The resulting regression model is used in order to up-scale the results from the micro-scale spatial window to the meso-scale level. As a demonstration, the procedure has been applied for the city of Addis Ababa, Ethiopia.

Electrically induced Bragg Modulator for ultrafast light modulation in Indium Phosphide devices

An electrically induced Bragg reflector modulator 2.5 mm long is been designed in InP/InGaAsP rib waveguide, which can theoretically reach ultra 40 GHz switching speed

Optimal Design of LIDs in Urban Stormwater Systems Using a Harmony-Search Decision Support System

During the last years, climate changes and urbanization are causing huge urban pluvial flood events in many countries in the world, driving to both develop and apply effective and innovative approaches for the design and management of urban stormwater systems. The gradual urbanization is provoking the increase of impervious surfaces and, consequently, of surface runoff and velocity and the reduction of concentration times of watersheds, both increasing soil erosion and worsening the water quality as a consequence of the intensive contamination. In this field, Low Impact Development (LID) practices for urban runoff control can be intended as an effective approach to both improve the urban resilience against the flooding risk and assure environmental interventions to adequate the urban stormwater systems to both climate and land use changes. In this paper, a Decision Support System (DSS) for the optimal design of LIDs in urban watershed is presented and discussed. The procedure is tested on Fuorigrotta (IT) and Ponticelli (IT) urban watersheds, with the aim of assessing the effectiveness of LIDs application in reducing both the flooded and conveyed volumes, at the expense of cost-effective solutions.