Highly Stretchable and Wearable Thermotherapy Pad with Micropatterned Thermochromic Display Based on Ag Nanowire–Single‐Walled Carbon Nanotube Composite

Due to the increasing interest in wearable devices, flexible and stretchable film heaters have been widely studied, as alternatives to heaters with conventional rigid shapes. Herein, a highly stretchable film heater (SFH) based on the silver nanowire (Ag NW)–single‐walled carbon nanotube composite with a thermochromic display on a polydimethylsiloxane (PDMS) substrate is successfully fabricated. The SFH shows excellent electrical conductivity, high mechanical stretchability, and outstanding reliability, with no significant degradation after 10 000 stretching cycles under tensile strain. The SFH can be heated to the target temperature (≈60 °C) within 30 s at a low applied voltage. In addition, a thermochromic display is fabricated to help prevent the risk of low‐temperature burns. Red (R), green (G), and blue (B) thermochromic microparticles (TMPs) are synthesized using drop‐based microfluidic technology. The TMPs show RGB colors at room temperature but change to a white color above a certain temperature. The TMPs are arrayed into a PDMS stencil on the basis of their particle sizes using the rubbing technique. The micropatterned thermochromic display, which functions as a visual alarm, combined with the SFH can pave the way for the development of thermotherapy pads for next‐generation wearable devices in the medical field.     

Biodegradable Polyanhydrides as Encapsulation Layers for Transient Electronics

Bioresorbable electronic systems represent an emerging class of technology of interest due to their ability to dissolve, chemically degrade, disintegrate, and/or otherwise physically disappear harmlessly in biological environments, as the basis for temporary implants that avoid the need for secondary surgical extraction procedures. Polyanhydride‐based polymers can serve as hydrophobic encapsulation layers for such systems, as a subset of the broader field of transient electronics, where biodegradation eventually occurs by chain scission. Systematic experimental studies that involve immersion in phosphate‐buffered saline solution at various pH values and/or temperatures demonstrate that dissolution occurs through a surface erosion mechanism, with little swelling. The mechanical properties of this polymer are well suited for use in soft, flexible devices, where integration can occur through a mold‐based photopolymerization technique. Studies of the dependence of the polymer properties on monomer compositions and the rates of permeation on coating thicknesses reveal some of the underlying effects. Simple demonstrations illustrate the ability to sustain operation of underlying biodegradable electronic systems for durations between a few hours to a week during complete immersion in aqueous solutions that approximate physiological conditions. Systematic chemical, physical, and in vivo biological studies in animal models reveal no signs of toxicity or other adverse biological responses.     

Preparation of tantalum nanopowders through hydrogen reduction of TaCl5 vapor

Tantalum powders, ranging from 14 to 56 nm in primary particle size, were produced through hydrogen reduction of TaCl₅ vapor in a furnace aerosol reactor. The mass of the precursor, solid TaCl₅, was instantaneously measured during vaporization with a load cell to determine and control the precursor concentration at the reactor inlet. Tantalum pentachloride to tantalum conversion was 35% and 98% at 1000 and 1400 °C, respectively. The primary particle size increased with increasing the evaporator temperature and the hydrogen flow rate. The tantalum powder produced was amorphous at 1000 °C and crystalline at 1400 °C. The XRD peaks of the as-produced powders shifted towards lower angles due to the partial dissolution of hydrogen in the tantalum. Upon removal of the hydrogen through heat treatment in a vacuum, the shift disappeared. The oxygen content of the powder was 6.0 to 6.9 wt.%, with an oxide layer about 3 nm thick formed on individual particles. Through thermogravimetric analysis in air, the powders were found to be resistant to further oxidation at up to 200 °C, but to have been completely oxidized at 400 °C.     

Uniform Coating of Nanometer-Scale BaTiO3 Layer on Spherical Ni Particles via Hydrothermal Conversion of Ti-Hydroxide

A uniform BaTiO₃ nano layer was coated on spherical Ni particles for multilayer ceramic capacitor applications via a Ti-hydroxide coating using the controlled hydrolysis of a TiCl₄ butanol solution containing (C₂H₅)₂NH (diethylamine, DEA) and its subsequent hydrothermal reaction at various [Ba(OH)₂], residual [DEA], and hydrothermal temperatures. The hydrothermal conversion was successful at [Ba(OH)₂]≥0.065 M (Ba/Ti≥1.3) and T ≥150°C, and the residual DEA in the Ti-hydroxide coating layer not only affected the formation of the BaTiO₃ phase but also resulted in a rough surface morphology. When a minimal amount of DEA was involved in the formation of Ti-hydroxide, a uniform BaTiO₃ coating with a clean surface morphology could be attained, which was confirmed by elemental mapping of the coated powder and the observation of hollow spheres after removing the Ni core. The BaTiO₃ coating was very effective not only in preventing Ni oxidation but also in shifting the starting point of Ni densification to a higher temperature.     

An overview of spectrum sensing techniques for cognitive LTE and LTE-A radio systems

Advanced communication systems, such as long term evolution (LTE) and LTE-advanced (LTE-A) systems, promise to increase the number of users with high-speed data exchange. However, it leads to spectrum scarcity because of the huge size of data exchange with limited spectrum resources. Cognitive radio (CR) technique is considered the best solution for this spectrum scarcity problem. Spectrum sensing (SS), one of the CR techniques is used to detect the spectrum hole of primary user (PU) without interference with PU. In this paper, several SS approaches for LTE and LTE-A systems are investigated in the CR system. These SS approaches are based on two techniques, namely energy detection and cyclostationary feature detection techniques. The first technique includes four approaches of auto-correlation based advanced energy, time domain detection, Welch periodogram and two-stage model algorithms, while the second technique contains two approaches, namely pilot induced cyclostationary and second order cyclostationary algorithms. According to the analysis, the two-stage model and the second order cyclostationary algorithms are better than the other algorithms because they produce accurate results at the expense of system complexity. Hence, in general a good SS algorithms would require some trade-off between complexity and accuracy.     

Analysis of V2V Broadcast Performance Limit for WAVE Communication Systems Using Two‐Ray Path Loss Model

The advent of wireless access in vehicular environments (WAVE) technology has improved the intelligence of transportation systems and enabled generic traffic problems to be solved automatically. Based on the IEEE 802.11p standard for vehicle‐to‐anything (V2X) communications, WAVE provides wireless links with latencies less than 100 ms to vehicles operating at speeds up to 200 km/h. To date, most research has been based on field test results. In contrast, this paper presents a numerical analysis of the V2X broadcast throughput limit using a path loss model. First, the maximum throughput and minimum delay limit were obtained from the MAC frame format of IEEE 802.11p. Second, the packet error probability was derived for additive white Gaussian noise and fading channel conditions. Finally, the maximum throughput limit of the system was derived from the packet error rate using a two‐ray path loss model for a typical highway topology. The throughput was analyzed for each data rate, which allowed the performance at the different data rates to be compared. The analysis method can be easily applied to different topologies by substituting an appropriate target path loss model.     

5.2 mW 61 dB SNDR 15 MHz Bandwidth CT ΔΣ Modulator Using Single Operational Amplifier and Single Feedback DAC

We propose an architecture that reduces the power consumption and active area of such a modulator through a reduction in the number of active components and a simplification of the topology. The proposed architecture reduces the power consumption and active area by reducing the number of active components and simplifying the modulator topology. A novel second‐order loop filter that uses a single operational amplifier resonator reduces the number of active elements and enhances the controllability of the transfer function. A trapezoidal‐shape half‐delayed return‐to‐zero feedback DAC eliminates the loop‐delay compensation circuitry and improves pulse‐delay sensitivity. These simple features of the modulator allow higher frequency operation and more design flexibility. Implemented in a 130 nm CMOS technology, the prototype modulator occupies an active area of 0.098 mm² and consumes 5.23 mW power from a 1.2 V supply. It achieves a dynamic range of 62 dB and a peak SNDR of 60.95 dB over a 15 MHz signal bandwidth with a sampling frequency of 780 MHz. The figure‐of‐merit of the modulator is 191 fJ/conversion‐step.     

Copolymerization of styrene and ethylene with mononuclear and dinuclear half-titanocenes

With mononuclear half-titanocenes such as CpTiCl₃, IndTiCl₃, and Me₅CpTiCl₃, as well as the constrained geometry catalyst (CGC) and a new dinuclear hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride) (TSDT), the copolymerization of styrene and ethylene was examined. The thermal properties and structure of copolymerization products were investigated with differential scanning calorimetry and ¹³C-nuclear magnetic resonance. In addition, the raw polymer was separated into homopolymer and copolymer with an extraction method and cross fractionation chromatography. With the above analysis, it was concluded that the raw polymer obtained with CpTiCl₃ and IndTiCl₃ was a mixture of syndiotactic polystyrene and polyethylene homopolymers with 10–30 wt % copolymer, whereas that produced by Me₅CpTiCl₃ and TSDT was a homopolymer mixture with a negligible amount of copolymer. Only CGC produced the copolymer of styrene and ethylene perfectly. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2187–2198, 1998     

Synthesis and characterization of novel aromatic-aliphatic poly(amide-imide-imide)s (PAII)

Novel poly(amide-imide-imide)s (PAII) were prepared by polycondensation of a new monomer synthesized from trimellitic anhydride and glutamic acid, followed by reflux condensing with thionyl chloride and several diamines. Polymers and monomers were characterized by ¹H NMR and FT-IR spectroscopy, elemental analysis and mass spectrometry. Inherent viscosities of the resulting polymers were in the range of 17–26 mL g^–1 (M_w 13 400–29 160, polydispersity (M_w/M_n) ca. 1.3–1.7), representing rather low molecular weights. The glass transition temperatures of the polymers were in the range of 210–285°C depending on the structure of diamines, and the thermal stability of the polymers was up to 400°C, comparable with that of polyimides and poly(amide imide)s. All the polymers synthesized are well soluble in aprotic polar solvents such as dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone and dimethylacetamide. Particularly, polymers containing oxydianiline and 4,4′-diaminodiphenyl sulfone were quite soluble in m-cresol, pyridine, nitrobenzene and tetrahydrofuran.