Fabrication of core-sheath nanoyarn via touchspinning and its application in wearable piezoelectric nanogenerator

Abstract

A simple and versatile touchspinning method is demonstrated for the fabrication of core-sheath nanofibrous piezoelectric yarns with a single filament electroconductive core. The polyvinylidene fluoride (PVDF) piezoelectric nanofibers are fabricated in a continuous spinning process with relatively controlled structure, orientation, and dimensions to form a sheath layer. The PVDF core-sheath nanoyarn is assembled into a piezoelectric nanogenerator (PNG) capable to convert mechanical energy of body motion into electricity. It was demonstrated that an electrical potential difference of 0.72?V can be generated under compression of 0.33?MPa for a single 3-cm long yarn. The touchspun nanoyarn fabrication method has great potential for the fabrication of functional smart textile products.     

Channel‐estimate‐based frequency‐domain equalization (CE‐FDE) for broadband single‐carrier transmission

A channel‐estimate‐based frequency‐domain equalization (CE‐FDE) scheme for wireless broadband single‐carrier communications over time‐varying frequency‐selective fading channels is proposed. Adaptive updating of the FDE coefficients are based on the timely estimate of channel impulse response (CIR) to avoid error propagation that is a major source of performance degradation in adaptive equalizers using least mean square (LMS) or recursive least square (RLS) algorithms. Various time‐domain and frequency‐domain techniques for initial channel estimation and adaptive updating are discussed and evaluated in terms of performance and complexity. Performance of uncoded and coded systems using the proposed CE‐FDE with diversity combining in different time‐varying, multi‐path fading channels is evaluated. Analytical and simulation results show the good performance of the proposed scheme suitable for broadband wireless communications. For channels with high‐Doppler frequency, diversity combining substantially improves the system performance. For channels with sparse multi‐path propagation, a tap‐selection strategy used with the CE‐FDE systems can significantly reduce the complexity without sacrificing the performance. Copyright © 2004 John Wiley & Sons, Ltd.     

Maximum Likelihood (ML) Symbol Timing Recovery (STR) Techniques for Reconfigurable PAM and QAM Modems

A fast symbol timing recovery (STR) scheme suitable for flexible-symbol-rate, burst-mode M-ary QAM (M-QAM) and PAM (M-PAM) demodulators used in broadband communications is proposed. The maximum- likelihood (ML) estimation is used to derive a feed-forward STR strategy to achieve fast and accurate derivation of the optimum timing instant with a very short training preamble for applications requiring short packet transmission. In addition, the signal sample at the optimum timing instant is reproduced by interpolation. Analysis to derive the ML-based timing estimation algorithm and STR structure is presented. Analytical models are developed to evaluate the effects of imperfect interpolation and channel additive white Gaussian noise (AWGN) on the timing estimation performance. The derived expressions can be used for optimum interpolation filter design and selection of key parameters to achieve the required mean squared timing error. Simulation results are in good agreement with the analytical prediction.     

Performance of an IJF-OQPSK Modem in Cascaded Nonlinear and Regenerative Satellite Systems

The probability of error (Pe) performance of an intersymbol-interference and jitter-free-offset QPSK (IJF-OQPSK) modem in conventional and regenerative satellite channels is studied and compared to that of a QPSK modem using computer simulation techniques. The results show that the IJF-OQPSK modem performs better than QPSK in both cascaded nonlinear channels and regenerative satellite links, especially with saturated earth station HPA and transponder TWTA.     

Crystal structure,magnetic properties,and magnetization variation in Bi0.84La0.16Fe1-xTixO3 polycrystalline ceramic

The crystal structure, microstructure, and magnetic properties of Bi_0.84La_0.16Fe_1-xTi_xO₃ (x?=?0.1, 0.14, 0.16, 0.2) ceramic samples prepared by solid-state reaction are investigated by combining X-ray diffraction, Raman scattering, scanning electron microscope, and magnetic measurements. The analysis of crystal structure reveals the presence of multiphase structures and the gradual formation of Aurivillus Bi₅FeTi₃O₁₅ phase when increasing Ti concentration. The microstructure study shows several grain shapes, corresponding to the different crystal structures and phases present in the sample. The competition in lattice strain of the coexisting phases leads to the isothermal structural transition and the self-change in magnetization. A drastic decrease in coercivity and an increase in magnetization are observed with increasing ferromagnetic-like hysteresis loops. The change in magnetic properties of the samples is strongly dependent on the coexisting phases in the samples.     

A List Sphere Decoding Algorithm with Improved Radius Setting Strategies

Complexity of different sphere-decoding (SD) algorithms is heavily influenced by their own distinctive computational features. Sphere radius setting for initialization and reduction during the search process, is one of the most important aspects affecting the SD efficiency. This paper examines radius setting strategies for list sphere-decoding (LSD) algorithms to calculate the soft-output information for coded systems, and proposes strategies to improve both the radius initialization and reduction in the original LSD algorithm. The proposed strategies can avoid the instability problem in the radius initialization of the original LSD algorithm and significantly increase its search efficiency as confirmed by simulation for both full-column-rank and underdetermined MIMO channels.     

Determining the number of zones in a pick-and-sort order picking system

In this study we consider a pick-and-sort order picking system, in which batches of orders are picked simultaneously from different (work) zones by a group of order pickers. After picking, the orders are transported by a conveyor to a next station for consolidation and packing. Packing can only occur when an order has been picked completely. For a given number of workers, each assigned to a single zone, a larger number of zones reduces pick time (since travel time reduces), but increases waiting time for completion at the packing stations, because more partial batches needing assembly arrive at the packing stations. Our aim is to determine the optimal number of zones such that the total (picking and packing) time to complete a batch is minimised. We solve this problem by optimally assigning items to pick routes in each zone. We illustrate the method with data taken from a distribution centre of one of the largest online retailers in The Netherlands.     

Opportunistic delay‐margin‐based resource allocation for next‐generation wireless networks

This paper studies and develops efficient traffic management techniques for downlink transmission at the base station (BS) of multi‐service IP‐based networks by combining quality‐of‐service (QoS) provision and opportunistic wireless resource allocation. A delay‐margin‐based scheduling (DMS) for downlink traffic flows based on the delays that each packet has experienced up to the BS is proposed. The instantaneous delay margin, represented by the difference between the required and instantaneous delays, quantifies how urgent the packet is, and thus it can determine the queuing priority that should be given to the packet. The proposed DMS is further integrated with the opportunistic scheduling (OPS) to develop various queueing architectures to increase the wireless channel bandwidth efficiency. Different proposed integration approaches are investigated and compared in terms of delay outage probability and wireless channel bandwidth efficiency by simulation. Copyright © 2010 John Wiley & Sons, Ltd.     

Bandwidth-efficient Bit-interleaved Coded Cooperative Communications

A cooperative coding scheme using M-ary modulation for high spectral efficiency and repetitive information transmission for diversity improvement is proposed. The encoder is a parallel concatenation of two bit-interleaved coded M-ary modulators (BICM) with scalable repetition of information symbols. As a result, the fraction of repeated information and the spectral efficiency of M-ary modulation can be used for bandwidth-performance tradeoff. Performance analysis is carried out to verify the performance advantage of the proposed system. In particular, analytical and simulation results in various block fading scenarios show that for a given bandwidth efficiency, a proper selection of the fraction of repeated information and the spectral efficiency of M-ary modulation can provide a large performance improvement.

Spreading profile of dopant solution on pre-sintered silica layers for selective area doping of integrated optic planar glass samples

The spread profile of potassium-permanganate (KMnO₄) dye on a porous pre-sintered silica layer deposited via Flame Hydrolysis Deposition is presented. The work is aimed at controlling the dopant profile on the resulting glass layer for optically passive and active devices integration. KMnO₄ is used as it allows visual qualification of its spread on the soot layer. Pre-sintered silica layers allow for application of dopants into the glass matrix via adsorption and pore retention. Selective area doping is achieved by applying specific volumes of the dye onto pre-selected areas on the sample using a micropipette. Higher dye volumes applied would result in larger spread diameters. Furthermore, control of the spread is possible by heating the sample during the application of the dye.