Quantum-corrected drift-diffusion models: Solution fixed point map and finite element approximation

This article deals with the analysis of the functional iteration, denoted Generalized Gummel Map (GGM), proposed in [C. de Falco, A.L. Lacaita, E. Gatti, R. Sacco, Quantum-Corrected Drift-Diffusion Models for Transport in Semiconductor Devices, J. Comp. Phys. 204 (2) (2005) 533–561] for the decoupled solution of the Quantum Drift-Diffusion (QDD) model. The solution of the problem is characterized as being a fixed point of the GGM, which permits the establishment of a close link between the theoretical existence analysis and the implementation of a numerical tool, which was lacking in previous non-constructive proofs [N.B. Abdallah, A. Unterreiter, On the stationary quantum drift-diffusion model, Z. Angew. Math. Phys. 49 (1998) 251–275, R. Pinnau, A. Unterreiter, The stationary current–voltage characteristics of the quantum drift-diffusion model, SIAM J. Numer. Anal. 37 (1) (1999) 211–245]. The finite element approximation of the GGM is illustrated, and the main properties of the numerical fixed point map (discrete maximum principle and order of convergence) are discussed. Numerical results on realistic nanoscale devices are included to support the theoretical conclusions.     

Large soluble groups and the control of embedding properties

The aim of this survey article is to show that the behaviour of subgroups of finite rank in a (generalized soluble) group of infinite rank can be neglected. Some new results on this subject are also presented.     

Magneto-optic effects in ferromagnetic films: Implications for spin devices

We present results on the magneto-optic properties of ferromagnetic films deposited on GaAs and SiO₂ substrates. Using left- and right-circularly polarized light, we have measured the polarization-dependent photoresponse and reflectivity of Co/GaAs, Fe/GaAs and NiFe/GaAs Schottky diodes and the polarization-dependent reflection and transmission of NiFe/SiO₂ and Co/SiO₂ structures as a function of ferromagnetic film thickness, reported here in the range of 7.5-15 nm. Films were prepared by sputtering and molecular-beam epitaxy. Measurements were made in the presence of magnetic fields ranging from −1.2 to +1.2 T both parallel and perpendicular to the sample surface. We find maximum polarization-dependent transmission and photoresponse effects (with respect to left- versus right-circularly polarized light) of 2-4% in magnitude. Taken together the work suggests that magneto-optic effects intrinsic to the films, rather than spin injection across the ferromagnetic/semiconductor interface, are responsible for the observed phenomenology. The work has direct implications for the interpretation of results in ferromagnetic/semiconductor spintronic systems.     

On vibrations due to vortex shedding induced on two cylinders with one in the wake of the other

Summary This paper follows a series of researchs concerning the vibrations induced on cylinders by the vortex shedding.The principal results of the previous researchs are first of all summarised.These researchs concerned the vibrations induced on a cylinder in a free stream, and the vibrations induced on a cylinder in the wake of a fixed one.Main purpose of the present paper is to describe the experimental results obtained on two cylinders, one in the wake of another, both vibrating. Many cases are considered either with equal or different frequencies.An analytical model simulating the phenomenon is here developped, the analytical results obtained are exposed and compared with the experimental ones.

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Sommario Questo lavoro segue una serie di ricerche sul fenomeno di distacco di vortici su un cilindro investito da una vena fluida ortogonale all'asse del cilindro stesso.Vengono in primo luogo riassunti i principali risultati delle precedenti ricerche riguardanti un cilindro vibrante in vena libera ed uno vibrante in scia di uno fisso.Scopo del presente lavoro è quello di riportare i risultati sperimentali relativi al caso di due cilindri, uno in scia di un altro, con frequenze uguali, di poco diverse o molto diverse.È stato inoltre elaborato un modello analitico per lo studio del fenomeno, il modello ed i risultati ottenuti sono pure riportati in questo lavoro.

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This work is the outcome of a collaboration between ENEL, Salvi S.p.A., the Institute of Applied Mechanics, University of Pavia and the Institute of Applied Mechanics, Polytechnic of Milan. Both the Institutes of Applied Mechanics received a CNR subsidy to take part in this research.     

Vortex ring/viscous wall layer interaction model of the turbulence production process near walls

An experimental simulation of the interaction of vortex ring-like eddies with the sublayer of a turbulent boundary layer is investigated. An artificially generated vortex ring interacting with a Stokes' layer enables investigation of the interaction with reproducible initial conditions and in the absence of background turbulence. All of the observed features in the turbulent boundary layer production process such as the streaky structure, the pockets, the hairpin vortices, streak lift-up, oscillation, and breakup, have been observed to form. The model shows us that hairpin vortices can pinchoff and reconnect forming new vortex ring-like eddies. Interestingly, the model includes interactions that occur with low probability in the turbulent boundary layer, but which contribute significantly to transport, and may be the events most readily controllable.     

Experimental characterization of ultrafine particle emissions from a light-duty diesel engine equipped with a standard DPF

A detailed experimental characterization of the particle emissions of a EURO 5 light-duty Diesel engine, equipped with a wall flow Diesel Particulate Filter (DPF), is presented. Particle Size Distributions (PSDs) in the range from 4.5 up to 160 nm have been measured at the engine exhaust by means of a Scanning Mobility Particle Sizer, during both DPF accumulation and regeneration phase. During accumulation, the size-dependent DPF removal efficiency has been evaluated by PSDs measurements at both inlet and outlet of the filter. The maximum efficiency was found in the range 10-40 nm. Nevertheless, the DPF ensures a strong reduction in the emissions for the sub-23 nm nanoparticles too, with an efficiency between 91–95%. Unless for the warm-up phase, the engine operating conditions do not have a great impact on the particles emitted due to the high DPF removal efficiency. The measurements carried out during the regeneration phase evidenced that particle emissions strongly depend on DPF temperature. Actually, once the soot burnout temperature is reached, soot oxidation starts and a great amount of particles in terms of PN is released. Overall, PSDs showed an increase in particle number concentration up to two order of magnitude with respect to the emissions measured during the accumulation phase.     

A functional iteration for the quantum drift–diffusion model: existence analysis and numerical approximation

This communication describes a functional iteration technique, denoted Generalized Gummel Map (GGM), for the solution of the Quantum Drift–Diffusion (QDD) model. The assumptions needed to establish existence of a fixed point for the GGM are described and their plausibility is assessed via physical arguments supported by one–dimensional numerical experiments. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of levamisole hydrochloride with HgI(2-)4 by a turbidimetric method and flow-injection analysis

This paper is concerned with the use of ion-association compounds in the analysis of pharmaceutical samples by FIA. The usual extraction into an organic phase is avoided by using turbidimetric detection. Determination of levamisole with HgI(2-)(4) has been developed as a practical example: the experimental variables were optimized by the modified simplex method. The calibration graph is linear over the levamisole concentration range 7-32 microg ml . The reproducibility (rsd) and injection sample rate are 0.9% and 80/hr, respectively.     

Thermally induced magnetic flux in a superconducting ring

The thermally induced magnetic flux in a bi-metallic superconducting loop of Nb and Ta has been measured and compared with theory. The predicted logarithmic divergence of the flux near the T_c of Ta is found, however the magnitude of the flux is larger than predicted.