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91.
Davide Cartasegna Piero Malcovati Lorenzo Crespi Kyehyung Lee Andrea Baschirotto 《Analog Integrated Circuits and Signal Processing》2014,78(3):785-798
This paper presents a design methodology for high-order class-D amplifiers, based on their similarity with sigma–delta ( $\Upsigma\Updelta$ ) modulators, for which established theory and toolboxes are available. The proposed methodology, which covers the entire design flow, from specifications to component sizing, is validated with three design examples, namely a second-order, a third-order, and a fourth-order class-D amplifier. Moreover, the third-order class-D amplifier has been integrated on silicon and characterized, further confirming the validity of the whole design flow. The achieved results demonstrate that high-order class-D amplifiers can achieve total-harmonic-distortion (THD) performance compatible with the specifications of high-end audio applications (THD ≈ 90 dB), which would be unfeasible with conventional first-order class-D amplifiers. 相似文献
92.
Gian Piero Celata Francesco Dannibale Andrea Chiaradia Maurizio Cumo 《International Journal of Heat and Mass Transfer》1998,41(24):396
The present work deals with the results of an experimental investigation on heat transfer in water cooled vertical pipes, for thermal–hydraulic conditions ranging from forced convective flow to mixed convective flow. The flow of water in the pipe is upwards.Experimental data confirm the reduction in the heat transfer rate for mixed convection in upward heat flow, mainly due to the laminarization effect in the near-wall region (buoyancy effect) . They are in a very good agreement with numerical methods, such as the k–-model.A new method for the calculation of the heat transfer coefficient in upward mixed convection heated flow is proposed. It is based on the well-known superposition method (heated downflow) modified accounting for the phenomenology of the upward heated flow in comparison with downflow heated conditions. 相似文献
93.
Fabio Nardone Gian Piero LignolaAndrea Prota Gaetano ManfrediAntonio Nanni 《Composite Structures》2011
An alternative to fiber reinforced polymer (FRP) materials adhesively bonded to the concrete substrate is the implementation of mechanically fastened FRP (MF-FRP) systems using steel anchors to secure the laminate to the substrate. The benefit of MF-FRP, compared to adhesive bonding for FRP flexural strengthening, is the speed of installation with unskilled labor, minimal or absent surface preparation under any meteorological condition and immediate use of the strengthened structures. Some of the potential shortcomings are: possible concrete damage during anchoring and limited opportunity of installation in the presence of congested internal reinforcement in the members to be strengthened. Laboratory testing and a number of field applications have shown the effectiveness of the MF-FRP method. In this paper, an analytical model is discussed for reinforced concrete (RC) members strengthened with MF-FRP strips. The model accounts for equilibrium, compatibility and constitutive relationships of the constituent materials; in particular, it accounts explicitly for the slip between the substrate surface and the FRP strip due to the behavior of the fasteners. The proposed flexural model, coupled with the computation algorithm, is able to predict the fundamentals of the behavior of RC flexural members strengthened with MF-FRP strips, in terms of both ultimate and serviceability limit states. Comparisons between the analytical predictions and the experimental results have been successfully performed. 相似文献
94.
Mechanistic studies of coal combustion have long highlighted the variety of reaction pathways along which gasification may take place. These involve chemisorption of reactants, formation of surface oxides, surface mobility of chemisorbed species, and product desorption. At the same time, exposure of the solid fuel to high temperatures is associated with solid-state thermally activated processes. Altogether, the course of gasification may be profoundly affected by the overlapping and interplay of heterogeneous oxidation with purely thermally activated solid-state reactions. In the present work the combustion of a South African bituminous coal is analyzed in the framework of a simplified reaction network that embodies heterogeneous oxidative and thermally activated processes (pyrolysis, thermal annealing, coal combustion, char combustion, oxygen chemisorption) active both on the raw coal and on its char. The kinetics of each process of the network is assessed by a combination of thermogravimetric and gas analysis on coal and char samples. The analysis is directed to the determination of the prevailing combustion pathway, established from the interplay of oxidative and solid-state thermally activated processes, as a function of combustion conditions (temperature, heating rate, particle size). 相似文献
95.
The current work investigates how personality and interpersonal processes combine to predict change in relationship quality. Measures of personality and emotion similarity were collected during laboratory interactions from a cross-sectional sample of dating couples (Study 1) and a 1-year longitudinal study of newlywed married couples (Study 2). Results showed that emotion similarity mediated the association between personality similarity and relationship quality (Studies 1 and 2) and that emotion convergence mediated the association between personality convergence and relationship satisfaction (Study 2). These results indicate that similarity and convergence in personality may benefit relationships by promoting similarity and convergence in partners' shared emotional experiences. Findings also lend support to models that integrate partners' enduring traits and couples' adaptive processes as antecedents of relationship outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
96.
Mauro Rajteri Claudio Gandini Eugenio Monticone Chiara Portesi Aldo Masoero Chiara Boveri Piero Mazzetti 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):351-353
In this paper we present some experimental results concerning the current noise produced during the resistive transition in MgB2 thin films. Preliminary investigations evidenced the presence of electrical noise whose power spectrum has a region of the 1/fn type with n 3. We suggest that the noise may originate from abrupt rearrangement of the current distribution inside the specimen during the percolative process of a diphasic system. Experimental measurements of the spectral components of the current noise taken during the resistive transition will be given and discussed. 相似文献
97.
Gian Luca Chiarello Ilenia Rossetti Paolo Lopinto Gabriele Migliavacca Lucio Forni 《Catalysis Today》2006,117(4):549-553
Perovskitic mixed oxides prepared through flame-spray pyrolysis possess a good stability in high-temperature application, viz. the catalytic flameless combustion of methane. Some preparation operating parameters are here analysed, such as O2 pressure drop along the spraying nozzle, O2 discharge velocity and flow rate. These parameters have been correlated with specific surface area, activity and durability of the prepared samples, as well as with flame temperature, varied by using different fuel mixtures. It was found that specific surface area increases with increasing O2 velocity and flow rate and with decreasing the combustion enthalpy of the solvent mixture. This reflects on both activity and durability of the catalyst. 相似文献
98.
A Padovani V Di Piero M Bragoni M Iacoboni GF Gualdi GL Lenzi 《Canadian Metallurgical Quarterly》1995,92(6):433-442
Left ventricular wall motion abnormalities secondary to stress-induced myocardial ischemia can be detected with difficulty by mentally comparing echocardiographic images sequentially recorded on videotape. Digital stress-echocardiography, a combination of ultrasound imaging and digital archiving technologies, at least partially can overcome this problem: the technique is based on reviewing images at rest and after stress (exercise or pharmacological) side by side in dual- or quad-screen digital format, in a synchronized cine-loop, as if obtained simultaneously. This technique however is presently not widely used, due to the high cost of most commercially available systems. We have developed a digital stress-echo system, which is easy to use and relatively inexpensive, running on a Macintosh II personal computer with 8-bit graphics. The 2-D echocardiographic images recorded on videotape are digitized offline using a video digitizing board. The image can be displayed and analyzed using the public domain NIH image software developed by Wayne Rasband, without loss in image quality and resolution, particularly if using Super-VHS videotape. We have made a macro procedure for the montage in a quad-screen format of four digital recorded echocardiographic cardiac cycles of six frames that takes only a little more time than commercially available systems. In conclusion, the use of a personal computer and low-cost software may help to make digital stress-echo techniques more widely feasible in the clinical setting and increase the diagnostic power of the ultrasound technique in the evaluation of patients with known or suspected coronary artery disease. 相似文献
99.
Analysis of the polar extracts from kancolla seeds led to the isolation of five betaines: glycine betaine, trigonelline, trigonelline methylester, trigonelline glucosylester and 3-carboxy-1-(2-sulfoethyl)-pyridinium, the last two of which have not previously been reported in the literature. All structures were elucidated from spectroscopic [NMR (1H, 13C, COSY, HOHAHA, HMQC, HMBC)] and mass spectrometric data (ESI-MS). 相似文献
100.
In this paper the contrasting effects of transmission impairments and capture on both the network and single user performance of a slotted Aloha system are investigated in a mobile radio environment, accounting for frequency non-selective random propagation phenomena, and employing the packet error probability in order to define packet losses and capture. With this study we demonstrate that it is possible to generalize in a real propagation context a method previously proposed in literature for evaluating the network behavior in terms of steady-state throughput, backlog and stability in conventional transmission conditions, i.e., when all the transmission channels were error-free and the collisions caused the loss of all the packets involved. Moreover, we indicate under which specific constraints on the terminal mobility we can apply this method to analytically predict the single user performance, which we show being an important design parameter. Through the numerical results reported we quantitatively point out that in the absence of coding capture increases system stability and moderately improves the overall system throughput and backlog. We also outline the trade-off between an increased capture gain obtained by means of coding and the corresponding system cost in terms of complexity and bandwidth occupancy. Furthermore, we demonstrate the unfairness which affects the single user performance and the consequent need for countermeasures in order not to discriminate among users differently located within the network; yet, this last solution is detrimental as regards the positive capture effects.This work was supported by M.U.R.S.T. and C.N.R. (Italy). 相似文献