276 research outputs found
Memory Devices: Part II – Non-Volatile Memories
No full textThis article illustrates the basic concepts underlying the operation of non-volatile memories (NVM). After a classification of NVMs based on their functional properties with respect to the programming and erasing operations, the treatment addresses the structure, operation principles, circuit organization and reliability issues of read-only memories (ROM), electrically programmable read-only memories (EPROM), electrically programmable and erasable read-only memories (EEPROM) and flash memories, including both the NOR and NAND organizations. A final section is devoted to non-conventional memories, including magnetic, ferroelectric and phase-change memories, which are still in an early development stage
A note on the fixed point for the polynomials of a boolean algebra with an operator of endomorphism
No full textWe study fixed point problem for boolean algebras with an endomorphism operator k. In particular we prove that in every finite algebra of this kind there exist polynomials f (x) (in which x only occurs within the scope of k) without fixed point. Some examples of Boolean algebras with endomorphism operator k in which every polynomial f (x) (in which x only occurs within the scope of k) has a fixed point are also given. Also we establish some properties of the algebras of this kind
Pseudo-shock waves and their interactions in high-speed intakes
No full textIn an air-breathing engine the flow deceleration from supersonic to subsonic conditions takes places inside the isolator through a gradual compression consisting of a series of shock waves. The wave system, referred to as a pseudo-shock wave or shock train, establishes the combustion chamber entrance conditions, and therefore influences the performance of the entire propulsion system. The characteristics of the pseudo-shock depend on a number of variables which make this flow phenomenon particularly challenging to be analysed. Difficulties in experimentally obtaining accurate flow quantities at high speeds and discrepancies of numerical approaches with measured data have been readily reported. Understanding the flow physics in the presence of the interaction of numerous shock waves with the boundary layer in internal flows is essential to developing methods and control strategies. To counteract the negative effects of shock wave/boundary layer interactions, which are responsible for the engine unstart process, multiple flow control methodologies have been proposed. Improved analytical models, advanced experimental methodologies and numerical simulations have allowed a more in-depth analysis of the flow physics. The present paper aims to bring together the main results, on the shock train structure and its associated phenomena inside isolators, studied using the aforementioned tools. Several promising flow control techniques that have more recently been applied to manipulate the shock wave/boundary layer interaction are also examined in this review
Automatic Optimization Algorithm for a Direct 2D and 3D Mesh Generation from the Layout Information
No full textA new algorithm has been designed and implemented, that allows for the automatic generation of an optimum 2D and 3D grid for device simulation from the information available at the circuit-layout level. The tool fills a gap in the top-down design chain of integrated circuits, easing the task of circuit designers who are often unaware of specific features of device-modeling tools
A quasi 2D semianalytical model for the potential profile in hetero and homojunction tunnel FETs
No full textA quasi 2D semianalytical model for the potential profile in hetero and homojunction tunnel FETs is developed and compared with full-quantum simulation data. It will be shown that the pure analytical solution perfectly matches the kp data at high VDS. However, a coupling with the numerical solution of the 1D Poisson equation in the transverse direction is necessary at low VDS, in order to properly describe the charge density in equilibrium with the drain contact. With such an approach we are able to correctly predict the potential profile for both the linear and saturation regimes
Effect of back-pressure forcing on shock train structures in rectangular channels
No full textThe deceleration of a supersonic flow to the subsonic regime inside a high-speed engine occurs through a series of shock waves, known as a shock train. The generation of such a flow structure is due to the interaction between the shock waves and the boundary layer inside a long and narrow duct. The understanding of the physics governing the shock train is vital for the improvement of the design of high-speed engines and the development of flow control strategies. The present paper analyses the sensitivity of the shock train configuration to a back-pressure variation. The complex characteristics of the shock train at an inflow Mach number M = 2 in a channel of constant height are investigated with two-dimensional RANS equations closed by the Wilcox k-ω turbulence model. Under a sinusoidal back-pressure variation, the simulated results indicate that the shock train executes a motion around its mean position that deviates from a perfect sinusoidal profile with variation in oscillation amplitude, frequency, and whether the pressure is first increased or decreased
Le valenze del corso di Laboratorio della Didattica delle Scienze matematiche, chimiche, fisiche e naturali nella formazione degli insegnanti specializzati della SSIS (sede di Ferrara)
No full textSi presentano esperienze didattiche su percorsi tematici a carattere integrato, progettate nel corso di laboratorio e successivamente sperimentate nell’ambito delle attività di tirocinio attivo. Si conclude con riflessioni sulla metodologia e sulle valenze della matematica e delle scienze integrate nella formazione dell’insegnante della SSIS
TCAD Modeling of High-Field Electron Transport in Bulk Wurtzite GaN: The Full-Band SHE-BTE
No full textGallium Nitride (GaN) High-Electron Mobility Transistors (HEMTs) actually represent one of the best candidates for medium-high power and radio frequency applications. As they operate at large bias and electric fields, a comprehensive analysis of the high-field transport properties is fundamentals, as hot electrons are expected to play a relevant role for the device reliability. In this perspective, Technology Computer-Aided Design (TCAD) simulations can be a very useful tool for the understanding of the phenomena dominating hot-electron degradation mechanisms. The most-accurate modeling approaches are based on the direct solution of the Boltzmann equation, which is not actually available for the GaN material. In this work, the deterministic solution of the Boltzmann transport equation via the spherical-harmonics expansion (SHE-BTE), as incorporated in a commercial TCAD tool, has been extended to the analysis of GaN electrons. To this purpose, the details of the full-band structure has been derived from DFT calculations as in state-of-art literature works, and the electron density of states, g(E), and group velocity g(E), have been calculated for the SHE-BTE for the first time. In addition to this, an accurate calibration of the total scattering rate accounting for nonpolar acoustic and optical carrier-phonon interaction, Coulomb scattering and impact ionization has been carried out against available Monte Carlo data and experiments. The proposed model is also shown to correctly predict the temperature dependence of the electron impact-ionization coefficient and current density up to breakdown
Experimental investigation on shock wave diffraction over sharp and curved splitters
No full textShock wave diffraction occurs when a normal travelling wave passes through a sudden area expansion. Turbulent, compressible, and vortical are the characterising adjectives that describe the flow features, which are slowly smeared out due to the dissipative nature of turbulence. The study of this phenomenon provides insight into several flow structures such as shear layer formation, vortex development, and vortex/shock interaction whose applications include noise control, propulsion or wing aerodynamics. A large amount of research has been carried out in the analysis of shock wave diffraction mainly around sharp wedges, but only few studies have considered rounded corners. This project has the aim to examine and compare the flow features which develop around three different geometries, ramp, symmetric and rounded, with experimental incident shock Mach numbers of 1.31 and 1.59, and Reynolds numbers of 1.08x106 and 1.68x106. Schlieren photography is used to obtain qualitative information about the evolution of the flow field. The results show that ramp and symmetrical wedges with a tip angle of 172° behave in the same manner, which exhibit clear dissimilarities with a curved corner. The flow field evolves more rapidly for a higher incoming Mach number which is also responsible for the development of stronger structures
Shock wave diffraction in the presence of a supersonic co-flow jet
No full textThe interaction between a diffracting shock wave and a uniform jet is a case that so far has only been partially investigated. This interaction is extremely important for the control of noise generation and improvement of combustor performance. To fill this knowledge gap, three geometries of the diffracting corner, namely a straight ramp, a serrated ramp, and a rounded corner, have been tested experimentally to study the interaction of shock diffraction with a supersonic co-flow jet at incident Mach numbers of 1.31 and 1.59, with Reynolds numbers of 1.08×1061.08×106 and 1.68×1061.68×106, respectively. Schlieren photography was employed to analyse the evolution of the flow phenomena. The aim is to provide a qualitative understanding of the interaction between the diffracting shock wave and the uniform jet relevant to future high-speed transport. The results show that the flow field evolves more rapidly and develops stronger structures for a higher shock Mach number. The diffraction around a rounded splitter develops a periodical vortical structure which continues after the disturbance introduced by the passage of the shock wave is removed
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