Novel Approach for Modeling Wireless Fading Channels Using a Finite State Markov Chain

Empirical modeling of wireless fading channels using common schemes such as autoregression and the finite state Markov chain (FSMC) is investigated. The conceptual background of both channel structures and the establishment of their mutual dependence in a confined manner are presented. The novel contribution lies in the proposal of a new approach for deriving the state transition probabilities borrowed from economic disciplines, which has not been studied so far with respect to the modeling of FSMC wireless fading channels. The proposed approach is based on equal portioning of the received signal‐to‐noise ratio, realized by using an alternative probability construction that was initially highlighted by Tauchen. The associated statistical procedure shows that a first‐order FSMC with a limited number of channel states can satisfactorily approximate fading. The computational overheads of the proposed technique are analyzed and proven to be less demanding compared to the conventional FSMC approach based on the level crossing rate. Simulations confirm the analytical results and promising performance of the new channel model based on the Tauchen approach without extra complexity costs.     

Throughput and Delay Analysis of IEEE 802.11 DCF in the Presence of Hidden Nodes for Multi-hop Wireless Networks

Hidden node collision in a contention-based medium access control protocol contributes to poor wireless network performance. This paper extended the Bianchi’s study and introduces a mathematical model that can be used to calculate throughput and delay for the IEEE 802.11 distributed coordination function of a multihop wireless network infrastructure assuming the presence of hidden node collision. This research investigates three essential parameters of multi-hop wireless networks. More specifically, this paper aims to analyze the effect of hidden nodes, network size, and maximum backoff stage on the overall system throughput and packet delay. Results clearly reveal the effect of large wireless network size, maximum backoff stage, and collision probability on throughput and packet delay. On one hand, throughput does not depend on the maximum backoff stage (m) for a small network size (e.g., n \(=\) 10). On the other hand, throughput does not strongly depend on the number of nodes when the backoff stage values are high. Comparing our proposed model in case single-hop with the Bianchi model, the analysis results indicate that the throughput values in our model when the numbers of nodes are 10, 50, and 100 are 0.6031, 0.4172 and 0.3433 respectively; whereas the throughput values are respectively 0.8370, 0.8317 and 0.8255 at the same number of nodes for the Bianchi model. The difference can be attributed to several assumptions made in our proposed model that were not considered in the Bianchi model.     

Synchrophasor communication

Synchronized phasor measurements provide the basis for fine-grained wide area power quality monitoring in electric grids. Time-synchronized phasor measurement units (PMUs) are deployed at different locations in the grid and report 10–60 measurements/second to energy management systems or other applications. For control applications it is crucial to receive measurement data as soon as possible after a state change in order to trigger corrective actions in time to prevent incidents in the grid. In this paper we analyze characteristics of synchrophasor M2M communication for different network technologies, including VDSL, HSPA and LTE networks. We briefly review synchrophasor communication approaches and real-time demands. We then emulate PMU traffic and perform measurements on different networks. We show how the underlying technology influences one-way delay patterns for synchrophasor communication, which has direct implication on the achievable real-time properties.     

A 0D Lead‐Free Hybrid Crystal with Ultralow Thermal Conductivity

Organic–inorganic hybrid materials are of significant interest owing to their diverse applications ranging from photovoltaics and electronics to catalysis. Control over the organic and inorganic components offers flexibility through tuning their chemical and physical properties. Herein, it is reported that a new organic–inorganic hybrid, [Mn(C₂H₆OS)₆]I₄, with linear tetraiodide anions exhibit an ultralow thermal conductivity of 0.15 ± 0.01 W m^?1 K^?1 at room temperature, which is among the lowest values reported for organic–inorganic hybrid materials. Interestingly, the hybrid compound has a unique 0D structure, which extends into 3D supramolecular frameworks through nonclassical hydrogen bonding. Phonon band structure calculations reveal that low group velocities and localization of vibrational energy underlie the observed ultralow thermal conductivity, which could serve as a general principle to design novel thermal management materials.     

Revamping SiO2 Spheres by Core–Shell Porosity Endowment to Construct a Mazelike Nanoreactor for Enhanced Catalysis in CO2 Hydrogenation to Methanol

Beyond the catalytic activity of nanocatalysts, the support with architectural design and explicit boundary could also promote the overall performance through improving the diffusion process, highlighting additional support for the morphology-dependent activity. To delineate this, herein, a novel mazelike-reactor framework, namely multi-voids mesoporous silica sphere (MVmSiO₂), is carved through a top-down approach by endowing core-shell porosity premade Stöber SiO₂ spheres. The precisely-engineered MVmSiO₂ with peripheral one-dimensional pores in the shell and interconnecting compartmented voids in the core region is simulated to prove combined hierarchical and structural superiority over its analogous counterparts. Supported with CuZn-based alloys, mazelike MVmSiO₂ nanoreactor experimentally demonstrated its expected workability in model gas-phase CO₂ hydrogenation reaction where enhanced CO₂ activity, good methanol yield, and more importantly, a prolonged stable performance are realized. While tuning the nanoreactor composition besides morphology optimization could further increase the catalytic performance, it is accentuated that the morphological architecture of support further boosts the reaction performance apart from comprehensive compositional optimization. In addition to the found morphological restraints and size-confinement effects imposed by MVmSiO₂, active sites of catalysts are also investigated by exploring the size difference of the confined CuZn alloy nanoparticles in CO₂ hydrogenation employing both in-situ experimental characterizations and density functional theory calculations.     

Interaction of α radiation with iron-doped n-type silicon

Deep-level transient spectroscopy (DLTS) measurements were carried out on low-doped n-silicon before and after irradiation with 5.48 MeV α particles at room temperature with a fluence of 10¹⁰ α particles/cm². The DLTS measurements on the samples identified three electron levels E₁, E₂ and E₃ before irradiation. The deep-levels characteristic studies include emission rate signatures, activation energies, defect concentrations and capture cross sections. It was found that all pre-existing defects decreased their amplitudes during irradiation. The decrease in activation energy of level E₃ and noticeable suppression of level E₁ was also observed after irradiation. It was clearly seen that the composite peak E₃ (combination of E₂ and E₃) was successfully resolved after irradiating with α particles. α-irradiation is seen to lead a significant suppression of the iron interstitial defect, and without causing any change in its room temperature annealing characteristics.     

Biomimetic Nanomaterial Strategies for Virus Targeting: Antiviral Therapies and Vaccines

The ongoing coronavirus disease 2019 (COVID-19) pandemic highlights the importance of developing effective virus targeting strategies to treat and prevent viral infections. Since virus particles are nanoscale entities, nanomaterial design strategies are ideally suited to create advanced materials that can interact with and mimic virus particles. In this progress report, the latest advances in biomimetic nanomaterials are critically discussed for combating viral infections, including in the areas of nanomaterial-enhanced viral replication inhibitors, biomimetic virus particle capture schemes, and nanoparticle vaccines. Particular focus is placed on nanomaterial design concepts and material innovations that can be readily developed to thwart future viral threats. Pertinent nanomaterial examples from the COVID-19 situation are also covered along with discussion of human clinical trial efforts underway that might lead to next-generation antiviral therapies and vaccines.     

Towards a Light Weight Routing Security in IoT Using Non-cooperative Game Models and Dempster–Shaffer Theory

Wireless Personal Communications - The internet of things (IoT) has become an emerging technology owing to the rapidly increasing number of devices and their connectivity to the internet. Routing...     

EMI Shielding Characteristics of Electrically Conductive Polymer Blends of PS/PANI in Microwave and IR Region

Conductive polymeric blends (CPBs) of polystyrene and polyaniline (PS/PANI) were prepared by solution casting method in various compositions. Film thickness of CPBs was achieved?～?250 micron. PS/PANI blend films were analyzed for electromagnetic interference (EMI) shielding characteristics in microwave and near-infrared (NIR) regions. PS/PANI blends showed remarkable features. Most mobile telecommunications use GHz frequency range and shielding effectiveness was observed in 9 GHz to 18 GHz. In 9 GHz to 18 GHz frequency range, 45 dB shielding effectiveness was measured. CPBs were also analyzed in the NIR region and showed transmittance of <1%. Microwaves and NIR radiation are the most abundant in the environment and cause damage to human health. Both types of radiation causes serious damage to electronic devices as well.

     

Preparation, Characterization, and Microwave Dielectric Properties of Sr2La3Nb1−x Ta x Ti4O17 (0 ≤ x ≤ 1) Ceramics

Sr₂La₃Nb_1?x Ta _x Ti₄O₁₇ (0 ≤ x ≤ 1) ceramics were processed via a solid-state mixed oxide route. Sr₂La₃Nb_1?x Ta _x Ti₄O₁₇ (0 ≤ x ≤ 1) solid solutions were single phase in the whole range of x values within the x-ray diffraction (XRD) detection limit. The microstructure comprised elongated and needle-shaped grains. The ceramics exhibit relative permittivity (ε _r) of 73 to 68.6, product of unloaded quality factor and resonant frequency (Q _u f ₀) of 7100 GHz to 9500 GHz, and temperature coefficient of resonant frequency (τ _f) of 78.6 ppm/°C to 56.6 ppm/°C.