Performance Optimization of Vertical Nanowire‐based Piezoelectric Nanogenerators

The integrated nanogenerator (NG) based on vertical nanowire (NW) arrays is one of the dominant designs developed to harvest mechanical energy using piezoelectric nanostructures. Finite element method (FEM) simulations of such a NG are developed using ZnO NWs in compression mode to evaluate its performances in term of piezoelectric potential generated, capacitance, induced mechanical energy, output electrical energy, and efficiency. This evaluation is essential to correctly understand NG operation. Three main issues are highlighted. The mechanical and electrical structures of the NG as an integrated system are optimized, and strategies for concentrating the mechanical strain field in the NWs and increasing the force sensitivity are developed. In addition, the influence of NWs length and diameter on NG performances is investigated. The optimization results in a piezoelectric nano composite material where global performances are improved by mean of long and thin NWs.     

Inter‐annual variability,risk and confidence intervals associated with propagation statistics. Part II: parameterization and applications

This set of two companion papers aims at providing a model for the inter‐annual variability of earth‐space propagation statistics and for the inherent risk and CIs. In part I, it was proposed to model the yearly variance σ² of empirical complementary CDFs so that where is the variance of estimation, the inter‐annual climatic variance and p the long‐term probability. Particularly, an analytical formulation of was derived and parameterized from synthetic rain attenuation data. Considering the statistical framework developed in part I, this part II is specifically devoted to the parameterization of the variance of estimation from experimental data of rain attenuation and rainfall rate. Then, a methodology to model and parameterize worldwide the inter‐annual climatic variance is presented. The model of yearly variance of the empirical complementary CDFs is finally compared against yearly experimental variances derived from data collected worldwide. The knowledge of this variability is very useful for system design as it allows the risk on a required availability and associated with a given propagation margin to be quantified. Copyright © 2013 John Wiley & Sons, Ltd.     

Selfishness in secure internet of things networks: 6TiSCH case study

Wireless Networks - Performance and communication security in the Internet of Things (IoT) area draw a major concern for both academic and industrial communities. Indeed, an emerging number of IoT...     

A closed-loop electrical stimulation system for cardiac cell cultures

An integrated electrical stimulation and recording system was designed for closed-loop control and analysis of cardiac cultures on planar microelectrode arrays. Stimulated action potentials from HL-1 clonal myocyte cultures were digitized, stimulation artifacts were removed using nulling and filtering methods, and analysis was performed to determine stimulation efficacy in real time. Results of this analysis were used to determine future stimulation waveform parameters such as polarity, amplitude, pulse duration, and rate or pattern. Algorithms were designed utilizing real-time analysis and control to maintain a desired electrophysiological response of the culture, such as an arbitrary capture fraction value. This paper presents the hardware and software design of the stimulus pulse circuitry, artifact extraction, analysis, and control components of the system. Applications of this technology include the study of cardiac cell physiology, improving the speed and accuracy of traditional open-loop stimulation protocols, pharmacological screening, and improving the performance of biosensors based on sensing electrical activity in cardiac cultures.     

Architecture of a Memory Manager for an MPEG-2 Video Decoding Circuit

A study of the MPEG-2 video decoding standard in Main Profile @ Main Level has been performed, comparing the different solutions existing for the VLSI implementation of the basic functions (Huffman decoding, IDCT...) included in the standard. Afterwards, a new dynamically configurable architecture is proposed for the memory manager, which is necessary to deal with the large data flow inside the decoder. It is aimed at interfacing the external memory, arbitrating the access requests coming from the different decoding units and allowing generic memory requests through the definition of virtual addresses. It is shown that, by means of a particular data organization, the circuit requires an external memory, which is a 2-MB DRAM in fast page or EDO mode, accessible via a 64-bit bus. The memory manager works at 27 MHz and allows a real-time decoding for MP @ ML bitstreams. It has been synthesized in a 0.8-m two-metal CMOS technology and presents a total area of 5.4 mm2 for 6500 gates.     

A physical optics approach to near field RCS computations

The scattered field of a perfectly conducting body treated using a physical optics approach is obtained in near field in either the monostatic or bistatic case. This approach opens new prospects for a broad range of applications in the areas of radar cross section (rcs) and antennas. Numerical examples for simple shapes (circular and rectangular plates) are given. Remarkable phenomena are found and discussed.     

Effects of photoperiod and pair-feeding on lactation of cows fed corn or barley grain in total mixed rations

Effects of photoperiod and type of grain were assessed using 47 cows (wk 1; 59.5 d of lactation) exposed daily to 16 h of light (long day) and fed randomly one of two diets containing an equal amount of cracked corn or rolled barley. During wk 5, cows were assigned within each diet to long day and ad libitum feeding, short day (8 h of light: 2 h of dark: 2 h of light: 12 h of dark) and ad libitum feeding, or long day and ad libitum feeding (wk 5 to 8) followed by pair feeding with short day cows between wk 9 and 16. Milk composition was not affected by treatments. Between wk 9 and 16, long day cows fed for ad libitum consumption or pair fed produced 5 to 11% more milk than cows exposed to short day; feed intake of long day cows fed for ad libitum consumption was greater than short short day and long day cows pair fed cows. Milk yield and total feed intake were not affected by type of grain in the diet. In conclusion, long day photoperiod increased milk yield and feed intake.     

A new concept of planar self-reconfigurable modular robot for conveying microparts

Modularity and self-healing are two interesting properties that could help to design more flexible conveyors of micro-objects. In the Smart Blocks project, we propose to design a 2D modular and self-reconfigurable robot composed of centimeter-scale sliding blocks that embed their own actuators and control electronics. This article presents a proof-of-concept of the linkage and of the traveling system as well as an algorithm able to reconfigure a set of blocks from a spatial configuration to another one. Prototype blocks have been realized using electro-permanent magnets which show a good motion speed while saving power consumption during the linkage. Our reconfiguration algorithm is implemented in a simulator software showing in real-time the reconfiguration of the robot.