Fast State-Space Harmonic-Distortion Estimation in Weakly Nonlinear Gm−C Filters

A fast, one-pass harmonic-distortion estimation algorithm for G _m-C filters is introduced. It is derived using state-space modeling and can be applied directly to G_m-C filters, of any order, with MOS transconductors exhibiting any type of weak nonlinearity. The algorithm is formed out of a small number of explicit expressions involving the filter's structural matrices and the transconductors' nonlinearity. It can be easily implemented in MATLAB. For verification of the theoretical development, the algorithm was used to derive the harmonic distortion of a single-ended G_m-C filter with weakly nonlinear transconductors designed on a 0.5-mum technology. The results of the algorithm and CADENCE simulation were found to be in good agreement     

Information capacity of nanowire crossbar switching networks

Crossbar switching networks formed by nanowires are promising future data storage devices. This work addresses the fundamental question: What is the information storage capacity of a crossbar switching network? The two major classes of nanowire crossbar switching networks are considered, those with ohmic and those with semiconductive switches. The focus is on the first class which is in the center of current nanotechnology research. Exact, simple approximate, and asymptotic expressions of the information storage capacity are provided as functions of the network size. The derivations indicate technological and geometrical considerations in the design of efficient nanowire devices     

Diophantine Frequency Synthesis for Fast-Hopping, High-Resolution Frequency Synthesizers

The application of the diophantine frequency synthesis (DFS) methodology is presented and certain practical aspects of it are illustrated through the design and frequency planning of two forward DFS synthesizers each using two Integer-N phase-locked loops (PLLs). Both synthesizers achieve frequency resolution about 100 times times better that their constituent PLLs without compromising hopping speed performance or spectral purity.     

Electronic word-of-mouth and online reviews in tourism services: the use of twitter by tourists

Lately, the online social media have revolutionized communications and consequently the marketing of tourism destinations and businesses. The area is rapidly evolving and the challenges and opportunities arising from it for tourism industry are already apparent. Electronic word-of-mouth (e-WOM) and online reviews/recommendations are increasingly used regarding tourism services that are high involvement services. The purpose of the present study is to develop a conceptual framework for understanding the foundations of digital communication and empirically investigate its validity by examining the factors influencing the tourism consumer behavior. This study adopts a conceptual model of e-WOM and explores the use of Twitter by the tourists. Findings revealed the factors affecting tourists’ decision-making and indicated that this social medium is not a panacea; it is another marketing channel to be wisely used in integrated communications marketing of tourism services.     

Liquid re-circulation in turbulent vertical pipe flow behind a cylindrical bluff body and a ventilated cavity attached to a sparger

The turbulent flow field (Re=60024) in the wake of a cylindrical bluff body in a 0.105 m internal diameter pipe with an area blockage ratio of 82% in turbulent single-phase flow was studied using laser Doppler velocimetry (LDV). The results for the time-averaged velocity showed a toroidal vortex below the bluff body. The axial location below the bluff body where both the time-averaged radial and axial velocity components were zero (eye of the vortex) was found at approximately 0.72D. The end of the re-circulation region as defined by a stagnation point on the centreline of the pipe was found at an axial location below the bluff body of approximately 1.3D. These two locations did not change when altering the liquid superficial velocity confirming that the geometry (i.e., size) of the toroidal vortex is not dependent on the superficial liquid velocity or the speed of the vortex.Similar measurements using LDV were taken in the wake of a ventilated cavity in a vertical 0.105 m internal diameter pipe, with an area blockage ratio of 80%. The flow beneath the cavity was turbulent two-phase bubbly flow and the liquid-only flow ahead of the cavity was turbulent (Re=45618). The cavity was attached to a (central) sparger, which is a scale-up of the design used by Bacon (1995). The average gas void fraction in the wake of the cavity was 7%. The results for the time-averaged velocity confirmed the formation of a toroidal vortex remarkably similar to the vortex formed below the bluff body. The eye of the vortex and the end of the re-circulation region were found at an axial location below the ventilated cavity of 0.78 and 1.35D, respectively, i.e., almost identical to the results for the bluff body.The LDV results of the cylindrical bluff body and the ventilated cavity were compared with the fully predictive model of the velocity distribution in the vortex proposed by Thorpe et al. (2001) and good agreement was found in both cases. The model also agreed well with the data of van Hout et al. (2002) for a Taylor bubble rising in stagnant liquid in a 0.025 m internal diameter pipe. The CFX simulations of Thorpe et al. (2001) carried out for a 0.050 m internal diameter pipe, agreed well with the experimental data of the cylindrical bluff body, the ventilated cavity and the data obtained by van Hout et al. (2002) when correlating the results in the appropriate dimensionless form. Our analysis showed that the maximum axial re-circulation velocity in the centre of the vortex ring was directly proportional to the mean velocity in the annulus at the base of the cylindrical bluff body, the ventilated cavity or the Taylor bubble. The proportionality constant for all cases was found to be approximately 0.38 confirming the value proposed by Thorpe et al. (2001).     

Sulfate resistance of limestone cement concrete exposed to combined chloride and sulfate environment at low temperature

Concrete durability was investigated, taking under consideration the limestone content of the cement used, as well as the effect of chlorides on concrete’s deterioration due to the thaumasite form of sulfate attack. A normal Portland cement and two Portland limestone cements (15% and 35% w/w limestone content) were used for concrete preparation. The specimens were immersed in two corrosive solutions (chloride-sulfate; sulfate) and stored at 5 ± 1 °C. Visual inspection of the specimens, mass measurements and compressive strength tests took place for 24 months. Concretes containing limestone, as cement constituent and/or as aggregate, suffered from the thaumasite form of sulfate attack, which was accompanied by brucite and secondary gypsum formation. Limestone cement concretes exhibited higher deterioration degree compared to the concrete made without limestone cement. The disintegration was more severe and rapid, the higher the limestone content of the cement used. Chlorides inhibit sulfate attack on concrete, thus delaying and mitigating its deterioration.