180 research outputs found
From kinetic models to hydrodynamics: some novel results
No full textFrom Kinetic Models to Hydrodynamics serves as an introduction to the asymptotic methods necessary to obtain hydrodynamic equations from a fundamental description using kinetic theory models and the Boltzmann equation. The work is a survey of an active research area, which aims to bridge time and length scales from the particle-like description inherent in Boltzmann equation theory to a fully established “continuum” approach typical of macroscopic laws of physics.The author sheds light on a new method—using invariant manifolds—which addresses a functional equation for the nonequilibrium single-particle distribution function. This method allows one to find exact and thermodynamically consistent expressions for: hydrodynamic modes; transport coefficient expressions for hydrodynamic modes; and transport coefficients of a fluid beyond the traditional hydrodynamic limit. The invariant manifold method paves the way to establish a needed bridge between Boltzmann equation theory and a particle-based theory of hydrodynamics. Finally, the author explores the ambitious and longstanding task of obtaining hydrodynamic constitutive equations from their kinetic counterparts. The work is intended for specialists in kinetic theory—or more generally statistical mechanics—and will provide a bridge between a physical and mathematical approach to solve real-world problems.
The Relationship between PM2.5 and PM10 in Central Italy: Application of Machine Learning Model to Segregate Anthropogenic from Natural Sources
No full textParticular Matter (PM) data are the most used for the assessment of air quality, but it is also useful to monitor VOC and CO. The health impact of PM increases with decreasing aerodynamic dimensions, therefore most of the monitoring is aimed at PM10 (fraction of PM with aerodynamic dimensions smaller than 10 µm) and PM2.5 (fraction with aerodynamic dimensions lower than 2.5 µm). Generally, anthropogenic emissions contribute mainly to PM2.5 levels, whereas natural sources can largely affect PM10 concentrations. PM2.5/PM10 ratio can be used as a proxy of the origin (anthropogenic vs natural) of the PM, providing a useful indication about the main sources of PM that characterizes a specific geographical or urban setting. This paper presents the results of the analysis of continuous measurements of PM10 and PM2.5 concentrations at eight stations of the regional air quality monitoring network in Abruzzo (Central Italy), in the period 2017–2018. The application of models based on machine learning technique shows that PM2.5/PM10 ratio can be used to classify PM emissions and to know the nature of the emission source (natural and anthropogenic), under determinate conditions, and properly taking into account the meteorological parameters
Robust LNA in GaN Technology
No full textLow noise amplifiers realized in GaN technology are focused starting from the basic technology and state-of-the-art amplifier realizations both in hybrid and, more in particular, monolithic form. System benefits are discussed, further detailing both robustness and survivability characteristics of GaN LNAs, together with actual performance
Allograft-Prosthetic Composite in the Proximal Tibia After Bone Tumor Resection
No full textWe consider an allograft-prosthesis composite in the proximal tibia one of the better reconstructive options in this site because it combines the mechanical stability of a prosthesis with the biologic reconstruction of the extensor mechanism. We retrospectively reviewed 62 patients who had proximal tibia reconstructions with allograft-prosthesis composites to ascertain the complications and functional outcomes. By combining an allograft with a prosthesis, placing cement in the graft, and press-fitting the prosthesis in the tibial diaphysis, we obtained satisfactory Musculoskeletal Tumor Society scores in 90.4% of patients, with a 5-year survival rate (73.4%) comparable to that of reconstruction with a modular prosthesis. However, we observed high infection rates (24.2%) and rotation of the medial gastrocnemius seemed not to reduce this complication. For this reason, we do not recommend using this reconstructive technique in patients who will receive postoperative chemotherapy or in patients in whom a previous reconstructive method failed. We believe the ideal candidate is the young patient with a benign aggressive or malignant low-grade tumor who has not undergone previous surgery.
Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.
Each author certifies that he or she has no commercial associations (e.g., consultancies, stock, ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.
Each author certifies that his or her institution has approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research
On the unconditional stability of N-port networks
No full textThis work reviews the topic of two-port unconditional stability (US) and fixes some misconceptions still common among high-frequency designers, notwithstanding the broad, relevant literature. Ohtomo's test for network stability is then presented in a synthetic form and linked to US conditions. Finally, this approach is extended to N-port networks to obtain two sets of US conditions, which are intuitive generalizations of results well known in the two-port case. These conditions represent a necessary complement to the few works which have discussed three-port US up to now, since they only focus on the geometrical part of the problem, omitting to explicitly take care of Rollett's proviso and its implications on US
Characterization and modelling of high-frequency active devices oriented to high-sensitivity subsystem design
No full textIn this chapter, quite a broad overview of noise characterization-related topics is offered to the reader, with different depth levels. Most of the attention, however, is paid to the practical side of noise measurements and the subsequent steps of noise extraction and modeling, as well as to some advanced design methodologies. A major concern is in the procedures that are necessary to effectively de-embed the measurements from the contribution of the test bench and the adopted methodologies. The scope of the discussion cover a well-assessed theory concerning linear devices operated in the frequency range from a few megahertz to some 100 GHz, and at physical temperatures above some tens of kelvins. In these conditions, 1/f noise can be neglected and Johnson (thermal) noise is approximately independent of frequency; as a consequence, thermal and, possibly, shot noise of elemental noise sources add up to yield a white power spectrum, which can be conveniently described in terms of “equivalent” thermal noise.
The second part of the chapter is devoted to the application of the device noise models in the proper design of single- and multistage low noise amplifiers, including a mixed technique that actually employs characterization techniques directly in the amplifier design
High spectral purity X- to W-band active GaAs monolithic frequency multiplier
No full textIn this contribution, an active high harmonic suppression x8 frequency multiplier using depletion-mode mHEMT devices and its design procedure are presented. The realized circuit exhibits 3 dB conversion gain in the 86.4 ÷ 91.2 GHz output frequency range, with 6 dBm output power. An harmonic suppression higher than 32 dBc has been achieved. The whole chip current consumption is 125 mA, occupying an area of 2.05 × 3.45 mm2. © 2014 IEEE
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