Effective Polysulfide Rejection by Dipole‐Aligned BaTiO3 Coated Separator in Lithium–Sulfur Batteries

Although the exceptional theoretical specific capacity (1672 mAh g^?1) of elemental sulfur makes lithium–sulfur (Li–S) batteries attractive for upcoming rechargeable battery applications (e.g., electrical vehicles, drones, unmanned aerial vehicles, etc.), insufficient cycle lives of Li–S cells leave a substantial gap before their wide penetration into commercial markets. Among the key features that affect the cyclability, the shuttling process involving polysulfides (PS) dissolution is most fatal. In an effort to suppress this chronic PS shuttling, herein, a separator coated with poled BaTiO₃ or BTO particles is introduced. Permanent dipoles that are formed in the BTO particles upon the application of an electric field can effectively reject PS from passing through the separator via electrostatic repulsion, resulting in significantly improved cyclability, even when a simple mixture of elemental sulfur and conductive carbon is used as a sulfur cathode. The coating of BTO particles also considerably suppresses thermal shrinkage of the poly(ethylene) separator at high temperatures and thus enhances the safety of the cell adopting the given separator. The incorporation of poled particles can be universally applied to a wide range of rechargeable batteries (i.e., metal‐air batteries) that suffer from cross‐contamination of charged species between both electrodes.     

Flat Frequency Comb Generation With an Integrated Dual-Parallel Modulator

A dual-parallel Mach-Zehnder modulator is employed to generate an optical frequency comb. Flat spectral response is obtained by optimizing the dc bias and the RF drive parameters of the device which is driven in the gigahertz frequency range. We demonstrate theoretically and experimentally, a flat spectral output across nine sidebands. A tunable multiwavelength source based on this approach allows for very precise wavelength spacing for dense wavelength-division-multiplexing applications and has the advantages of efficiency and simplicity.     

Making Large‐Area Titanium Disulfide Films at Reduced Temperature by Balancing the Kinetics of Sulfurization and Roughening

The synthesis of large‐area TiS₂ thin films is reported at temperatures as low as 500 °C using a scalable two‐step method of metal film deposition followed by sulfurization in an H₂S gas furnace. It is demonstrated that the lowest‐achievable sulfurization temperature depends strongly on the oxygen background during sulfurization. This dependence arises because Ti? O bonds present a substantial kinetic and thermodynamic barrier to TiS₂ formation. Lowering the sulfurization temperature is important to make smooth films, and to enable integration of TiS₂ and related transition metal dichalcogenides—including metastable phases and alloys—into device technology.     

The Impact of Cooperative Nodes on the Performance of Vehicular Delay-Tolerant Networks

Vehicular communications refer to a wide range of networks proposed for environments characterized by sparse connectivity, frequent network partitioning, intermittent connectivity, long propagation delays, asymmetric data rates, and high error rates. These environments may also be characterized by a potential non-available end-to-end path. To overcome these issues and improve the overall network performance, cooperation between network nodes must be severely considered. Nodes may cooperate by sharing their storage capacity, bandwidth, or even energy resources. However, nodes may be unwilling to cooperate due to a selfish behavior or to an intent to protect the integrity of their own resources. This selfish behavior significantly affects the functionality and performance of the network. This paper overviews the most recent advances related with cooperation on vehicular networks. It also studies the impact of different cooperation levels in the performance of Vehicular Delay-Tolerant Networks (VDTNs). It was shown that scenarios with a higher number of cooperative nodes present the best results in terms of bundle delivery delay.     

Facile Fabrication and Superparamagnetism of Silica‐Shielded Magnetite Nanoparticles on Carbon Nitride Nanotubes

Using conventional methods to synthesize magnetic nanoparticles (NPs) with uniform size is a challenging task. Moreover, the degradation of magnetic NPs is an obstacle to practical applications. The fabrication of silica‐shielded magnetite NPs on carbon nitride nanotubes (CNNTs) provides a possible route to overcome these problems. While the nitrogen atoms of CNNTs provide selective nucleation sites for NPs of a particular size, the silica layer protects the NPs from oxidation. The morphology and crystal structure of NP–CNNT hybrid material is investigated by transmission electron microscopy (TEM) and X‐ray diffraction. In addition, the atomic nature of the N atoms in the NP–CNNT system is studied by near‐edge X‐ray absorption fine structure spectroscopy (nitrogen K‐edge) and calculations of the partial density of states based on first principles. The structure of the silica‐shielded NP–CNNT system is analyzed by TEM and energy dispersive X‐ray spectroscopy mapping, and their magnetism is measured by vibrating sample and superconducting quantum interference device magnetometers. The silica shielding helps maintain the superparamagnetism of the NPs; without the silica layer, the magnetic properties of NP–CNNT materials significantly degrade over time.     

High Efficiency Perovskite Solar Cells Exceeding 22% via a Photo-Assisted Two-Step Sequential Deposition

One of the most effective methods to achieve high-performance perovskite solar cells (PSCs) is to employ additives as crystallization agents or to passivate defects. Tri-iodide ion has been known as an efficient additive to improve the crystallinity, grain size, and morphology of perovskite films. However, the generation and control of this tri-iodide ion are challenging. Herein, an efficient method to produce tri-iodide ion in a precursor solution using a photoassisted process for application in PSCs is developed. Results suggest that the tri-iodide ion can be synthesized rapidly when formamidinium iodide (FAI) dissolved isopropyl alcohol (IPA) solution is exposed to LED light. Specifically, the photoassisted FAI–IPA solution facilitates the formation of fine perovskite films with high crystallinity, large grain size, and low trap density, thereby improving the device performance up to 22%. This study demonstrates that the photoassisted process in FAI dissolved IPA solution can be an alternative strategy to fabricate highly efficient PSCs with significantly reduced processing times.     

Overview of the MPEG Reconfigurable Video Coding Framework

Video coding technology in the last 20 years has evolved producing a variety of different and complex algorithms and coding standards. So far the specification of such standards, and of the algorithms that build them, has been done case by case providing monolithic textual and reference software specifications in different forms and programming languages. However, very little attention has been given to provide a specification formalism that explicitly presents common components between standards, and the incremental modifications of such monolithic standards. The MPEG Reconfigurable Video Coding (RVC) framework is a new ISO standard currently under its final stage of standardization, aiming at providing video codec specifications at the level of library components instead of monolithic algorithms. The new concept is to be able to specify a decoder of an existing standard or a completely new configuration that may better satisfy application-specific constraints by selecting standard components from a library of standard coding algorithms. The possibility of dynamic configuration and reconfiguration of codecs also requires new methodologies and new tools for describing the new bitstream syntaxes and the parsers of such new codecs. The RVC framework is based on the usage of a new actor/ dataflow oriented language called CAL for the specification of the standard library and instantiation of the RVC decoder model. This language has been specifically designed for modeling complex signal processing systems. CAL dataflow models expose the intrinsic concurrency of the algorithms by employing the notions of actor programming and dataflow. The paper gives an overview of the concepts and technologies building the standard RVC framework and the non standard tools supporting the RVC model from the instantiation and simulation of the CAL model to software and/or hardware code synthesis.     

Review of different classes of RFID authentication protocols

Radio-frequency identification (RFID) is an up-and-coming technology. The major limitations of RFID technology are security and privacy concerns. Many methods, including encryption, authentication and hardware techniques, have been presented to overcome security and privacy problems. This paper focuses on authentication protocols. The combination of RFID technology being popular but unsecure has led to an influx of mutual authentication protocols. Authentication protocols are classified as being fully fledged, simple, lightweight or ultra-lightweight. Since 2002, much important research and many protocols have been presented, with some of the protocols requiring further development. The present paper reviews in detail recently proposed RFID mutual authentication protocols, according to the classes of the authentication protocols. The protocols were compared mainly in terms of security, the technique that they are based on, protocols that the presented protocol has been compared with, and finally, the method of verifying the protocol. Important points of the comparisons were collected in two tables.

     

Attention-based video streaming

This paper considers the problem of video streaming in low bandwidth networks and presents a complete framework that is inspired by the fovea–periphery distinction of biological vision systems. First, an application specific attention function that serves to find the important small regions in a given frame is constructed a priori using a back-propagation neural network that is optimized combinatorially. Given a specific application, the respective attention function partitions each frame into foveal and periphery regions and then a spatial–temporal pre-processing algorithm encodes the foveal regions with high spatial resolution while the periphery regions are encoded with lower spatial and temporal resolution. Finally, the pre-processed video sequence is streamed using a standard streaming server. As an application, we consider the transmission of human face videos. Our experimental results indicate that even with limited amount of training, the constructed attention function is able to determine the foveal regions which have improved transmission quality while the peripheral regions have an acceptable degradation.