Combustion Synthesized Zinc Oxide Electron‐Transport Layers for Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) have advanced rapidly with power conversion efficiencies (PCEs) now exceeding 22%. Due to the long diffusion lengths of charge carriers in the photoactive layer, a PSC device architecture comprising an electron‐ transporting layer (ETL) is essential to optimize charge flow and collection for maximum performance. Here, a novel approach is reported to low temperature, solution‐processed ZnO ETLs for PSCs using combustion synthesis. Due to the intrinsic passivation effects, high crystallinity, matched energy levels, ideal surface topography, and good chemical compatibility with the perovskite layer, this combustion‐derived ZnO enables PCEs approaching 17–20% for three types of perovskite materials systems with no need for ETL doping or surface functionalization.     

Pressure‐Tunable Ambipolar Conduction and Hysteresis in Thin Palladium Diselenide Field Effect Transistors

Few‐layer palladium diselenide (PdSe₂) field effect transistors are studied under external stimuli such as electrical and optical fields, electron irradiation, and gas pressure. The ambipolar conduction and hysteresis are observed in the transfer curves of the as‐exfoliated and unprotected PdSe₂ material. The ambipolar conduction and its hysteretic behavior in the air and pure nitrogen environments are tuned. The prevailing p‐type transport observed at atmospheric pressure is reversibly turned into a dominant n‐type conduction by reducing the pressure, which can simultaneously suppress the hysteresis. The pressure control can be exploited to symmetrize and stabilize the transfer characteristics of the device as required in high‐performance logic circuits. The transistors are affected by trap states with characteristic times in the order of minutes. The channel conductance, dramatically reduced by the electron irradiation during scanning electron microscope imaging, is restored after an annealing of several minutes at room temperature. The work paves the way toward the exploitation of PdSe₂ in electronic devices by providing an experiment‐based and deep understanding of charge transport in PdSe₂ transistors subjected to electrical stress and other external agents.     

Very Low Voltage MOS Translinear Loops Based on Flipped Voltage Followers

A novel technique for operating MOS Translinear loops at very low supply voltages is described, based on the use of Flipped Voltage Followers for biasing the loops. The resulting topologies, suited to standard CMOS processes, can be successfully applied to a varied repertory of low-voltage analog circuits, such as squarers, multipliers, filters, oscillators, and RMS-DC converters. Measurement results for a geometric-mean and a squarer/divider circuit demonstrate on silicon the usefulness of this technique.     

利用KPI调试和优化UMTS网络

从语音到视频到网上游戏,UMTS网络提供了各种客户服务,对移动网络运营商来说,调试或优化网络正变得越来越复杂.网络运营商一直把传统网络的主要性能指标(KPI)看作理解和调试网络性能的工具.     

A distributed data storage protocol for heterogeneous wireless sensor networks with mobile sinks

This paper presents ProFlex, a distributed data storage protocol for large-scale Heterogeneous Wireless Sensor Networks (HWSNs) with mobile sinks. ProFlex guarantees robustness in data collection by intelligently managing data replication among selected storage nodes in the network. Contrarily to related protocols in the literature, ProFlex considers the resource constraints of sensor nodes and constructs multiple data replication structures, which are managed by more powerful nodes. Additionally, ProFlex takes advantage of the higher communication range of such powerful nodes and uses the long-range links to improve data distribution by storage nodes. When compared with related protocols, we show through simulation that Proflex has an acceptable performance under message loss scenarios, decreases the overhead of transmitted messages, and decreases the occurrence of the energy hole problem. Moreover, we propose an improvement that allows the protocol to leverage the inherent data correlation and redundancy of wireless sensor networks in order to decrease even further the protocol’s overhead without affecting the quality of the data distribution by storage nodes.     

Pacemaker interference by magnetic fields at power line frequencies

Human exposure to external 50/60-Hz electric and magnetic fields induces electric fields within the body. These induced fields can cause interference with implanted pacemakers. In the case of exposure to magnetic fields, the pacemaker leads are subject to induced electromotive forces, with current return paths being provided by the conducting body tissues. Modern computing resources used in conjunction with millimeter-scale human body conductivity models make numerical modeling a viable technique for examining any such interference. In this paper, an existing well-verified scalar-potential finite-difference frequency-domain code is modified to handle thin conducting wires embedded in the body. The effects of each wire can be included numerically by a simple modification to the existing code. Results are computed for two pacemaker lead insertion paths, terminating at either atrial or ventricular electrodes in the heart. Computations are performed for three orthogonal 60-Hz magnetic field orientations. Comparison with simplified estimates from Faraday's law applied directly to extracorporeal loops representing unipolar leads underscores problems associated with this simplified approach. Numerically estimated electromagnetic interference (EMI) levels under the worst case scenarios are about 40 microT for atrial electrodes, and 140 microT for ventricular electrodes. These methods could also be applied to studying EMI with other implanted devices such as cardiac defibrillators.     

A 0.8 μm CMOS testable switched-capacitor filter for video frequency applications

This paper presents the design of a fifth-order low-pass elliptic filter that employs a parallel connection of two all-pass sections to satisfy specifications commonly used in video frequency applications. Operating with a sampling frequency of 16 MHz, the IC prototype was implemented in a standard double-poly CMOS 0.8 μm process. The experimental verification showed a passband frequency deviation smaller than 0.08 dB up to the passband edge frequency of 3.4 MHz, and an output noise power of 0.97 ${\mu {\rm V}_{\rm RMS}}/{\sqrt {Hz}}This paper presents the design of a fifth-order low-pass elliptic filter that employs a parallel connection of two all-pass sections to satisfy specifications commonly used in video frequency applications. Operating with a sampling frequency of 16 MHz, the IC prototype was implemented in a standard double-poly CMOS 0.8 μm process. The experimental verification showed a passband frequency deviation smaller than 0.08 dB up to the passband edge frequency of 3.4 MHz, and an output noise power of 0.97 , resulting in a dynamic range of 49.1 dB. The filter structure enables multiple fault detection and suits modern automated testing configurations to allow accurate estimation of the actually implemented transfer function parameters, an issue of increasing importance in VLSI circuit design. The relative area required for testing the fifth-order filter is only 8% of the total filter area, and decreases as the filter order increases. Jorge Morales Ca?ive was born in Cienfuegos, Cuba, in 1963. He received the B.Sc. and M.Sc. degrees from the Technical University of San Petersburg, Russia, in 1986 and 1988, respectively, and the D.Sc. degree from the Federal University of Rio de Janeiro, Brazil, in 1991, all in electrical engineering. From 1988 to 1994, he worked at CEADEN, in Havana, Cuba, on the development of nuclear equipments. From 1994 to 1997, he worked at INOR, in Havana, Cuba, on the research and development of acquisition systems and image processing for nuclear medicine. His research interests are in the areas of analog and digital signal processing. Antonio Petraglia (S’89-M’91-SM’99) received the Engineer and M.Sc. degrees from the Federal University of Rio de Janeiro (UFRJ), Brazil, in 1977 and 1982, respectively, and the Ph.D. degree from the University of California, Santa Barbara (UCSB), in 1991, all in electrical engineering. In 1979, he joined the Faculty of UFRJ as an Associate Professor of electrical engineering, where he served as a Co-Chair in the Department of Electronic Engineering from 1982 to 1984. During the second semester of 1991, he was a post-Doctoral researcher with the Department of Electrical and Computer Engineering at UCSB. Since 1992 he has been on the faculty of the Program for Post-Graduate Engineering at UFRJ, where in 1997 he established the Laboratory for the Processing of Analog and Digital Signals. From March 2001 through March 2002 he was a Visiting Scholar with the Electrical Engineering Department at the University of California, Los Angeles. He has been involved in teaching and research activities in the areas of analog and digital signal processing, and in mixed analog-digital integrated circuit design. He is a distinguished member of the Brazilian Millenium Group in Nanoelectronics and Microelectronics in 2006-2008. Dr. Petraglia served as an Associate Editor for the IEEE Transactions on Circuits and Systems-II: Analog and Digital Signal Processing in 2002–2003 Mariane Rembold Petraglia (M’97) received the B.Sc. degree in electronic engineering from the Federal University of Rio de Janeiro, Brazil, in 1985, and the M.Sc. and Ph.D. degrees in electrical engineering from the University of California, Santa Barbara, in 1988 and 1991, respectively. From 1992 to 1993, she was with the Department of Electrical Engineering, Catholic University of Rio de Janeiro, Brazil. Since 1993, she has been with the Department of Electronic Engineering and with the Program of Electrical Engineering, COPPE, at the Federal University of Rio de Janeiro, where she is presently an Associate Professor. From March 2001 to February 2002, she was a Visiting Researcher with the Adaptive Systems Laboratory, at the University of California, Los Angeles. Her research interests are in adaptive signal processing, multirate systems, and image processing. Dr. Petraglia is a member of Tau Beta Pi, and a distinguished member of the Brazilian Millenium Group in Nanoelectronics and Microelectronics in 2006–2008. She is serving as an Associate Editor for the IEEE Transactions on Signal Processing since Nov. 2004.     

Buffer losses vs. deadline violations for ABR traffic in an ATM switch: A computational approach

The B‐ISDN will carry a variety of traffic types: the Variable Bit Rate traffic (VBR), of which compressed video is an example, Continuous Bit Rate traffic (CBR), of which telemetry is an example, Data traffic, and Available Bit Rate traffic (ABR) that represents aggregate data traffic with very limited guarantees on quality. Of these, VBR and CBR have timing constraints and need synchronous bandwidth; data traffic is relatively delay insensitive. In this paper, we consider the VBR, Data and ABR traffic types and obtain the cumulative distribution function (cdf) of the queueing delay experienced by a burst of ABR traffic in the output buffer of an ATM switch. The cdf is used to trade off buffer loss probabilities against deadline violation probabilities through adjusting the buffer size and (delay) deadline values. Large buffers result in low losses but queueing delays can become excessive and cause a high level of deadline violations. Both losses and violations are detrimental and an operating point must be chosen to achieve a balance. In this paper we study the nature of the trade off. We develop a stochastic Petri net model assuming periodic burst arrivals for VBR and Poisson arrival processes for the Data and ABR traffic types at the burst level, and solve the model analytically (numerically) using a decomposition approach. This decomposition, along with the inherent decomposability of the tagged customer approach for obtaining the cdf opens up a possibility of carrying out fast computations using a parallel machine for selecting the operating point each time that a call is admitted. This revised version was published online in June 2006 with corrections to the Cover Date.     

Control mechanisms to improve the robustness of mpeg-2 based communications over ATM networks

Audio-visual and other multimedia services are seen as an important source of traffic for ATM networks. Due to the statistical multiplexing schemes used by ATM networks, cells are exposed to delays, jitters and losses. These phenomena affect the quality of the service provided to the video-based applications. In this paper, we introduce a set of control mechanisms at different levels of the protocol architecture. These mechanisms have been particularly tailored to better support MPEG-2-based video communications applications using ATM networks as their underlying transmission mechanism. We show that the use of errorconcealment mechanisms prove more effective when supplemented by a structured set of protocol mechanisms. We study the impact of cell losses on the quality of MPEG-2 video sequences and provide an evaluation of the quality of the decoded video as perceived by the end user. Our results demonstrate the effectiveness of the proposed protocol architecture in improving the quality of service provided to the video application.     

Crystal Size,Morphology, and Growth Mechanism in Bio‐Inspired Apatite Nanocrystals

Bio‐inspired apatite nanoparticles precipitated in the presence of citrate ions at increasing maturation times are characterized in terms of structure, size, morphology, and composition through advanced X‐ray total scattering techniques. The origin of the platy crystal morphology, breaking the hexagonal symmetry, and the role of citrate ions is explored. By cross‐coupling the size and shape information of crystal domains with those obtained by atomic force microscopy on multidomain nanoparticles, a plausible mechanism underlying the amorphous‐to‐crystal transformation is reconstructed. In the present study, citrate plays the distinct roles of inducing the platy morphology of the amorphous precursor and controlling the thickness of the Ca‐deficient apatite nanocrystals. These findings can open new scenarios also in bone mineralization, where citrate might have a broader role to play than has been thought to date.