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Search Results: 1 - 10 of 401394 matches for " M. Ravaioli "
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Modelling approach to the assessment of biogenic fluxes at a selected Ross Sea site, Antarctica
M. Vichi,A. Coluccelli,M. Ravaioli,F. Giglio
Ocean Science Discussions (OSD) , 2009,
Abstract: Several biogeochemical data have been collected in the last 10 years of Italian activity in Antarctica (ABIOCLEAR, ROSSMIZE, BIOSESO-I/II). A comprehensive 1-D biogeochemical model was implemented as a tool to link observations with processes and to investigate the mechanisms that regulate the flux of biogenic material through the water column. The model is ideally located at station B (175° E–74° S) and was set up to reproduce the seasonal cycle of phytoplankton and organic matter fluxes as forced by the dominant water column physics over the period 1990–2001. Austral spring-summer bloom conditions are assessed by comparing simulated nutrient drawdown, primary production rates, bacterial respiration and biomass with the available observations. The simulated biogenic fluxes of carbon, nitrogen and silica have been compared with the fluxes derived from sediment traps data. The model reproduces the observed magnitude of the biogenic fluxes, especially those found in the bottom sediment trap, but the peaks are markedly delayed in time. Sensitivity experiments have shown that the characterization of detritus, the choice of the sinking velocity and the degradation rates are crucial for the timing and magnitude of the vertical fluxes. An increase of velocity leads to a shift towards observation but also to an overestimation of the deposition flux which can be counteracted by higher bacterial remineralization rates. Model results suggest that the timing of the observed fluxes depends first and foremost on the timing of surface production and on a combination of size-distribution and quality of the autochtonous biogenic material. It is hypothesized that the bottom sediment trap collects material originated from the rapid sinking of freshly-produced particles and also from the previous year's production period.
Study of Warm Electron Injection in Double Gate SONOS by Full Band Monte Carlo Simulation
G. Giusi,G. Iannaccone,M. Mohamed,U. Ravaioli
Physics , 2008, DOI: 10.1109/LED.2008.2004784
Abstract: In this paper we investigate warm electron injection in a double gate SONOS memory by means of 2D full-band Monte Carlo simulations of the Boltzmann Transport Equation (BTE). Electrons are accelerated in the channel by a drain-to-source voltage VDS smaller than 3 V, so that programming occurs via electrons tunneling through a potential barrier whose height has been effectively reduced by the accumulated kinetic energy. Particle energy distribution at the semiconductor/oxide interface is studied for different bias conditions and different positions along the channel. The gate current is calculated with a continuum-based post-processing method as a function of the particle distribution obtained from Monte Carlo. Simulation results show that the gate current increases by several orders of magnitude with increasing drain bias and warm electron injection can be an interesting option for programming when short channel effects prohibit the application of larger drain bias.
Il Servizio Biblioteche della provincia di Ravenna
Licia Ravaioli
Conservation Science in Cultural Heritage : Historical Technical Journal , 2007,
Simulation of Biological Ionic Channels by Technology Computer-Aided Design
K. Hess,U. Ravaioli,M. Gupta,N. Aluru,van der Straaten,R. S. Eisenberg
VLSI Design , 2001, DOI: 10.1155/2001/25603
Abstract: This paper discusses the use of established Technology Computer-Aided Design (TCAD) tools and methodologies for the study of charge transport in molecular biology systems, like ionic channels, that display a behavior analogous to electronic devices. Continuum drift-diffusion and Monte Carlo methods can be applied to analyze steady-state and transient behavior of ionic channels over time scales that cannot be resolved practically by detailed molecular dynamics or quantum approaches. The difficult ion-water interaction can be lumped phenomenologically into mobility or scattering rate parameters, while the solution of Poisson equation over the complete domain provides a simple way to include external boundary conditions and image force effects at dielectric discontinuities. We present here some recent results of 3-D simulations for a gramicidin ion channel, obtained using the rapid prototyping computational platform PROPHET.
Three-dimensional Spectral Solution of Schr?dinger Equation
A. Trellakis,U. Ravaioli
VLSI Design , 2001, DOI: 10.1155/2001/76808
Abstract: We present a fast and robust method for the full-band solution of Schrödinger's equation on a grid, with the goal of achieving a more complete description of high energy states and realistic temperatures. Using Fast Fourier Transforms, Schrödinger's equation in the one band approximation can be expressed as an iterative eigenvalue problem for arbitrary shapes of the conduction band. The resulting eigenvalue problem can then be solved using Krylov subspace methods as Arnoldi iteration. We demonstrate the algorithm by presenting an example concerning non-parabolic effects in an ultra-small Metal-Oxide-Semiconductor quantum cavity at room-temperature. For this structure, we show that the non-parabolicity of the conduction band results in a significant lowering of high-energy electronic states.
Full Band Monte Carlo Simulation of Electron Transport in Ge with Anisotropic Scattering Process
RAVAIOLI Umberto,Chen Yong,RAVAIOLI Umberto,

半导体学报 , 2005,
Abstract: The electron transport properties in Ge are calculated by full band Monte Carlo technique with anisotropic scattering consideration.The calculation procedures are as follows:the full band structure is calculated by nonlocal empirical pseudopotential approach;the relative value of density of state (DOS) is computed by counting the number of states located in a certain region of the energy;the phonon dispersion curve is obtained from an adiabatic bondcharge model;the electron-phonon scattering rates are approximated by the nonparabolic model derived from Fermi’s golden rule at low energy region and scaled by DOS at higher energy region;the energy and momentum conservations are employed for choosing the final state after scattering.The validity of this Monte Carlo simulator and the physical models that are used is fully confirmed by comparing the program output to experimental results listed in references.As this Monte Carlo model can accurately reproduce the velocity and energy characteristics of electrons in Ge and the DOS scaled scattering rate can significantly reduce the computational cost for scattering rates,this approach is suitable for device simulation.
Efficient Silicon Device Simulation with the Local Iterative Monte Carlo Method
Jürgen Jakumeit,Torsten Mietzner,Umberto Ravaioli
VLSI Design , 2001, DOI: 10.1155/2001/27920
Abstract: The Local Iterative Monte Carlo technique (LIMO) is used for an effective simulation of hot electron distributions in silicon MOSFETs. This new Monte Carlo approach yields an efficient use of the computational resources due to a different iteration scheme. In addition the necessary computation time can be further reduced by a reuse of the computational expensive MC step simulation results in the iteration process. The later possibility is investigated in detail in this work. Results for short channel MOSFETs demonstrates that correct two-dimensional hot electron distributions can be calculated by LIMO within 1 hour on a standard work station.
Influence of Electron-Electron Interaction on Electron Distributions in Short Si-MOSFETs Analysed Using the Local Iterative Monte Carlo Technique
T. Mietzner,J. Jakumeit,U. Ravaioli
VLSI Design , 2001, DOI: 10.1155/2001/68217
Abstract: The effects of electron–electron interaction on the electron distribution in n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) are studied using the Local Iterative Monte Carlo (LIMO) technique. This work demonstrates that electron–electron scattering can be efficiently treated within this technique. The simulation results of a 90 nm Si-MOSFET are presented. We observe an increase of the high energy tail of the electron distribution at the transition from channel to drain.
Cluster-based Parallel 3-D Monte Carlo Device Simulation
Asim Kepkep,Umberto Ravaioli,Brian Winstead
VLSI Design , 2001, DOI: 10.1155/2001/70635
Abstract: The recent improvements in the performance of commodity computer have created very favorable conditions for building high performance parallel machines from computer clusters. These are very attractive for 3-D device simulation, necessary to model properly carrier-carrier interaction and granular doping effects in deeply scaled silicon devices. We have developed a parallel 3-D Monte Carlo simulation environment customized for clusters using the Message Passing Library (MPI). The code has been tested on the supercluster of NCSA at the University of Illinois. We present here test results for an n-i-n diode structure, along with an analysis of performance for two different domain decomposition schemes.
Quantum Potential Approaches for Nano-scale Device Simulation
Hideaki Tsuchiya,Brian Winstead,Umberto Ravaioli
VLSI Design , 2001, DOI: 10.1155/2001/73145
Abstract: With the progress of integrated technology, the feature size of experimental electron devices have already been scaled down deeply into the sub–0.1 μm region. For such ultra-small devices, it is increasingly important to take quantum mechanical effects into account for device simulation. In this paper, we present a new approach for quantum modeling, applicable to multi-dimensional ultra-small device simulation. In this work, the quantum effects are represented in terms of quantum mechanically corrected potential in the classical Boltzmann equation. We apply the Monte Carlo method to solve the quantum transport equation, and demonstrate that the quantum effects such as tunneling and quantum confinement effects can be incorporated in the standard Monte Carlo techniques.
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