A Reconfigurable Low-Noise Amplifier Using a Tunable Active Inductor for Multistandard Receivers

A reconfigurable low-noise amplifier (LNA) based on a high-value active inductor (AI) is presented in this paper. Instead of using a passive on-chip inductor, a high-value on-chip inductor with a wide tuning range is used in this circuit and results in a decrease in the physical silicon area when compared to a passive inductor-based implementation. The LNA is a common source cascade amplifier with RC feedback. A tunable active inductor is used as the amplifier output load, and for input and output impedance matching, a source follower with an RC network is used to provide a 50 Ω impedance. The amplifier circuit has been designed in 0.18 µm CMOS process and simulated using the Cadence Spectra circuit simulator. The simulation results show a reconfigurable frequency from 0.8 to 2.5 GHz, and tuning of the frequency band is achieved by using a CMOS voltage controlled variable resistor. For a selected 1.5 GHz frequency band, simulation results show S ₂₁ (Gain) of 22 dB, S ₁₁ of ?18 dB, S ₂₂ of ?16 dB, NF of 3.02 dB, and a minimum NF (NFmin) of 1.7 dB. Power dissipation is 19.6 mW using a 1.8 V dc power supply. The total LNA physical silicon area is (200×150) µm².     

An improved thermal and electrical model for a solar photovoltaic thermal (PV/T) air collector

In this paper, an attempt is made to investigate the thermal and electrical performance of a solar photovoltaic thermal (PV/T) air collector. A detailed thermal and electrical model is developed to calculate the thermal and electrical parameters of a typical PV/T air collector. The thermal and electrical parameters of a PV/T air collector include solar cell temperature, back surface temperature, outlet air temperature, open-circuit voltage, short-circuit current, maximum power point voltage, maximum power point current, etc. Some corrections are done on heat loss coefficients in order to improve the thermal model of a PV/T air collector. A better electrical model is used to increase the calculations precision of PV/T air collector electrical parameters. Unlike the conventional electrical models used in the previous literature, the electrical model presented in this paper can estimate the electrical parameters of a PV/T air collector such as open-circuit voltage, short-circuit current, maximum power point voltage, and maximum power point current. Further, an analytical expression for the overall energy efficiency of a PV/T air collector is derived in terms of thermal, electrical, design and climatic parameters. A computer simulation program is developed in order to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Finally, parametric studies have been carried out. Since some corrections have been down on thermal and electrical models, it is observed that the thermal and electrical simulation results obtained in this paper is more precise than the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency and overall energy efficiency of PV/T air collector is about 17.18%, 10.01% and 45%, respectively, for a sample climatic, operating and design parameters.     

Recent Advances on Vibration Control of Structures Under Dynamic Loading

In this paper, a review of recent journal articles on passive, active, semi-active, and hybrid vibration control of structures subjected to dynamic loading is presented. Passive systems reviewed include tuned mass damper (TMD), tuned liquid column damper (TLCD), tuned liquid column ball damper (TLCBD), circular TLCD (CTLCD), and pendulum TLCD (PTLCD). Active control systems include active tuned mass dampers (ATMD) and piezoelectric actuators. Semi-active systems include magnetorheological (MR) damper, negative stiffness devices (NSD), magneto-rheological damper TMD (MR-TMD), variable stiffness semi-active TMD (VS-STMD), variable damper STMD (VD-STMD), and recentering variable friction device (RVFD). Hybrid systems include active base isolation system and semi-active MR dampers with nonlinear base isolators. The current frontier of research is semi-active control of structures as well hybridization of various control systems. The problem is complex requiring integration of several different hardware and software technologies with structural design such as smart materials, adaptive dampers, actuators, sensors, and control and signal processing algorithms. This complexity also makes it an exciting area of research and development.     

Synthesis of fluorescent ABA triblock copolymer via click reaction

A hyperbranched–linear–hyperbranched (ABA) triblock copolymer containing poly(ethylene glycol) (PEG) as linear block and polyglycerol (hbPG) as hyperbranched blocks has been synthesized through a copper‐catalysed click reaction. In order to synthesize the hyperbranched block, propargyl alcohol‐initiated ring‐opening multibranching polymerization of glycidol was used to prepare hbPG with the propargyl segment in the focal point (CH?C? hbPG). Separately, PEG was functionalized at both ends using cyanuric chloride, and then the chloride groups of cyanuric chloride were substituted by azide groups. Finally, the azide‐functionalized PEG was conjugated to CH?C? hbPG via a click reaction. Substitution of the chlorine atoms of cyanuric chloride under different conditions together with click chemistry allows the synthesis of a variety of polymeric architectures. In the last step, fluorescein was attached to the block copolymer as a fluorescent probe in order to study the cell internalization of this copolymer. This type of triblock copolymer is a promising future nanomaterial for simultaneous drug delivery and cell imaging. © 2016 Society of Chemical Industry     

Fundamental period of irregular concentrically braced steel frame structures

This paper presents the results of investigation on the fundamental periods of concentrically braced frame (CBF) structures with varying geometric irregularities. A total of 12 CBFs are designed and analyzed. On the basis of the results obtained from vibration theory, equations for the approximate fundamental periods are put forth for CBFs, which take into account vertical and horizontal irregularities. Through statistical comparison, it was found that a three‐variable power model that is able to account for irregularities resulted in a better fit to the Rayleigh data than equations that were dependent on height only. The proposed equations were validated through a comparison of available measured period data for CBFs. These proposed equations will allow design engineers to quickly and to accurately estimate the fundamental period of CBF structures by taking into account irregularities. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimal control of adaptive building structures under blast loading

>Creation of a new generation of high-performance adaptivesmart structures with self-modification capability is advanced to resist dynamic loadings due to both nature such as wind and earthquake loadings and man such as blast and bomb loadings. The general computational models and high-performance parallel algorithms developed recently by the authors for optimal control of large structures are applied to multistorey building structures subjected to blast loadings. Both internal blast loading at different floor levels and external blast loading from outside the structure are considered. Results are presented for several regular and irregular moment-resisting steel space frame structures. It is demonstrated that the response of a building structure to blast loadings can be reduced substantially to a fraction of the response of the uncontrolled structure. © 1998 Elsevier Science Ltd. All rights reserved.     

Minimum Weight Design of Large Structures on a Network of Workstations

Abstract: Advances in performance of local area networks and microprocessors are providing significant computational capability at a relatively low cost. This paper is concerned with development of a distributed algorithm for minimum weight design of large structures on a network of workstations using biologically inspired genetic algorithms. Communication constructs from the software library Parallel Virtual Machine (PVM) have been used for message passing between the workstations. The algorithm has been applied to minimum weight design of two example structures. Performance estimates are provided based on the granularity and parallelization efficiency of the distributed model. The speedup of the distributed algorithm increases with the size of the structure, making it particularly suitable for optimization of large structures. For large structures, a high average speedup of about 10 is achieved using 11 workstations. The high scalability of the distributed genetic algorithm demonstrates that a cluster of workstations provides a cost-effective alternative for high-performance computing for coarse-grained applications such as the GA-based structural optimization.     

Wavelet energy spectrum for time‐frequency localization of earthquake energy

The authors recently developed a method for time‐frequency signal analysis of earthquake records using Mexican hat wavelets. Ground motions in earthquakes are postulated as a sequence of simple penny‐shaped ruptures at different locations along a fault line and occurring at different times. In this article, a wavelet energy spectrum is proposed for time‐frequency localization of the earthquake input energy. The ground acceleration generated by a simple penny‐shaped rupture is used as the basis to form the mother wavelet. The symmetric Mexican hat wavelet is chosen as the mother wavelet. The spectrum is presented pictorially in a two‐dimensional, time‐frequency domain. The proposed wavelet energy spectrum can be used to observe the evolution of the frequency contents of earthquake energy over time and distance of the site from the epicenter in a more accurate manner than the traditional time series (accelerogram) or frequency domain (Fourier amplitude spectrum) representation. It can be viewed as a microscope for looking into the time‐frequency characteristics of earthquake acceleration records. The wavelet energy spectrum provides frequency evolution information to be used in the structural design process. © 2003 Wiley Periodicals, Inc. Int J Imaging Syst Technol 13, 133–140, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10038