Design and realization of low profile dual-wideband monopole antenna incorporating a novel ohm (Ω) shaped DMS and semi-circular DGS for wireless applications

In this paper, a compact microstrip line fed dual-wideband printed monopole antenna (PMA) for wireless communication applications is presented. The proposed antenna consists of an asymmetric rectangular patch via a microstrip-fed line, an ohm (Ω) shaped DMS loaded at the rectangular patch, and dual semi-circular shaped DGS embedded in the partial rectangular ground plane. The combination of an ohm shaped DMS and two semi-circular DGS is used to broaden the bandwidth of the two bands and improve the return loss for the desired antenna. The measured 10 dB bandwidth for return loss are achieved to be 21.52% (3.40–4.22 GHz) and 47.32% (5–8.1 GHz) in the lower and upper band, respectively which covers the bandwidth requirements of 5.2/5.8 GHz WLAN and 3.5/5.5 GHz Wi-MAX application bands. Furthermore, the proposed antenna has a very simple planar structure and occupies a small area of only 621 mm² (23 mm × 27 mm). The proposed antenna has a desirable VSWR level, radiation pattern, radiation efficiency and gain characteristics which are suitable for wireless communication applications.     

A new approach to the design and analysis of peer‐to‐peer mobile networks

This paper introduces a new model and methodological approach for dealing with the probabilistic nature of mobile networks based on the theory of random graphs. Probabilistic dependence between the random links prevents the direct application of the theory of random graphs to communication networks. The new model, termed Random Network Model, generalizes conventional random graph models to allow for the inclusion of link dependencies in a mobile network. The new Random Network Model is obtained through the superposition of Kolmogorov complexity and random graph theory, making in this way random graph theory applicable to mobile networks. To the best of the authors' knowledge, it is the first application of random graphs to the field of mobile networks and a first general modeling framework for dealing with adhoc network mobility. The application of this methodology makes it possible to derive results with proven properties. The theory is demonstrated by addressing the issue of the establishment of a connected virtual backbone among mobile clusterheads in a peertopeer mobile wireless network. Using the Random Network Model, we show that it is possible to construct a randomized distributed algorithm which provides connectivity with high probability, requiring exponentially fewer connections (peertopeer logical links) per clusterhead than the number of connections needed for an algorithm with a worst case deterministic guarantee.     

A theoretical study of the asymmetric excitation of conducting flanges by a primary aperture antenna and the consequent radiation pattern†

The excitation of a conducting flange, asymmetric both in length of the flange elements and orientation with respect to the axis of the primary aperture antenna, is considered theoretically. Assuming the two edges of the flanges as two linear secondary sources excited by the primary antenna, the resultant radiation pattern is derived.     

Hall of fame for mobile commerce and its applications: A bibliometric evaluation of a decade and a half (2000–2015)

This study intends to evaluate the current development and trends of researches on mobile commerce and its applications through bibliometric analysis. Several publication characteristics were examined, on top of lists for most cited articles on this area and most studied mobile commerce applications. Through the data gathered from Web of Science database, this study employs several measures, namely impact factor, h-index, and citation counts to evaluate the productivity, impact, and research performance of countries, journals, authors, and research institutions. The number of publications are increasing yearly, with USA leading most of the times. Several international collaboration patterns were identified, and surprisingly some Asian countries have comparable performance to Western countries, in terms of the measures employed. Likewise, Asian authors and research institutions are found to have outstanding achievements too. Moreover, both the most studied mobile commerce applications and most cited lists offer some future directions. This study serves as a forerunner in using bibliometric analysis to evaluate researches on mobile commerce and its applications, and expected to benefit researchers in the area of mobile commerce, by identifying potential research directions. In addition, this study also serves as a useful guide to potential researchers and practitioners. However, improvements could be made, if extra analyses, such as content analysis, are added in.     

Implementation of an SDR platform using GPU and its application to a 2?��?2 MIMO WiMAX system

Conventional communication systems have been implemented using digital signal processors (DSPs) and/or field programmable gate arrays (FPGAs), especially for software defined radio (SDR) functionality. We propose a scheme that uses a graphics processing unit (GPU) in place of the conventional DSPs or FPGAs for the implementation of an SDR-based communication system. The GPU, a high-speed parallel processor with multiple arithmetic logic units, is adopted for the signal processing of the physical layer required for the parallel processing in an SDR system. The compute unified device architecture (CUDA) based on the C language provides a software development kit (SDK) for the modem application of the GPU. Therefore we utilize the CUDA SDK to implement the real-time modem function. This paper presents an implementation of a 2 × 2 multiple-input multiple-output (MIMO) WiMAX system employing a GPU as the real-time modem. By installing a radio frequency module on top of the GPU modem, we implement a real-time transmission system for video data. The performance of the proposed GPU-based system is demonstrated by comparing its operation time against that of the conventional DSP-based system.     

Aggregation-Induced Emission in a Flexible Phosphine Oxide and its Zn(II) Complexes—A Simple Approach to Blue Luminescent Materials

Easily accessible blue-emitting materials are in the focus of ongoing research, as they still lack the efficiency and lifetime of their red and green counterparts. The new multidentate phosphine oxide ligands and two respective ZnCl₂ complexes presented here combine a straightforward synthesis with high yields and show interesting luminescent properties. The free ligand exhibits blue luminescence in the crystalline state, but not in amorphous films or diluted solution. In contrast, the Zn(II) complexes shows intense blue luminescence in the crystalline state as well as in amorphous thin films and in solution. Fluorescence lifetime imaging microscopy measurements show luminescence lifetimes of 3–6 ns indicative of fluorescence. By combining the experimental data with quantum chemical calculations, we propose a model where the conformation of the molecule is restricted, either via the crystal environment, aggregation, or the steric fixation by the coordinating central atom, blocking the nonradiative relaxation from the excited into the ground electronic state. However, this nonradiative relaxation is still possible in the gas phase via elongation of a P C bond. These results may provide a general mechanism to explain the luminescence properties in a whole class of organic phosphine oxides.     

A Novel Approach to Open “Dead Space” and Modify Interfacial Features of Carbon Nanotube Assemblies by a Microwave Shock

Despite 30-year development of carbon nanotube (CNT) based materials, harnessing the outstanding nanoscale properties of individual CNT for macroscale applications remains challenging. High specific surface area, a crucial feature of CNTs, often suffers from the formation of tightly packed bundles with inaccessible “dead space”. Herein, a novel “microwave shock” approach to open the “dead space” trapped within bundles is reported. Employing N₂ ambient during microwave irradiation, CNT bundles undergo an efficient structural alteration and interfacial modification simultaneously due to the strong radiative coupling, while the graphitic structure remains undamaged. In this way, a 15-fold increase (from 42 to 648 m² g⁻¹) in the interstitial surface area as well as the lithiophilic functionalization (≈1 atom% nitrogen doping) are achieved without the degradation of other properties. Furthermore, to highlight the merits of this microwave shock process, the treated CNT films are applied as a host material for the anode in a lithium metal battery and demonstrate the suppression of dendritic lithium growth and improve cycling stability. This microwave shock approach provides an efficient avenue to modify nanocarbon-based materials for further applications.