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.     

Highly Power‐Efficient Rack‐Level DC Power Architecture Combined with Node‐Level DC UPS

This letter presents a highly efficient rack‐level DC power architecture combined with a node‐level DC uninterruptible power supply (UPS). The proposed system can provide almost the equivalent power efficiency of a high‐voltage DC data center without any change in the existing power infrastructure. The node‐level DC UPS combined with a power distribution board provides high power efficiency as well as lower UPS installation costs. Implemented on a rack, the entire power system can be monitored through a network.     

Crystallographic, Thermoelectric, and Mechanical Properties of Polycrystalline Ba8Al x Si46−x Clathrates

The Al content dependence of crystallographic, thermoelectric, and mechanical properties is reported for polycrystalline Ba₈Al _x Si_46?x (nominal x = 15 to 17) clathrates prepared by combining arc melting and spark plasma sintering methods. The elastic constants and the coefficient of thermal expansion (CTE), which are also important properties for designing thermoelectric devices, are presented. Powder x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy (EDX) indicate that the type I clathrate is the major phase of the samples but impurity phases (mainly BaAl₂Si₂, Si, and Al) are included in the samples with high Al contents. The actual Al content x determined by EDX ranges from approximately 14 to 15. The absolute value of the Seebeck coefficient increases and the electrical conductivity decreases as the Al content increases. The changes in Seebeck coefficient and electrical conductivity are explained in terms of the dependence of the carrier concentration on the Al content. The elastic constants and the CTE of the samples depend weakly on the Al content. Some of the properties are compared with reported data of single crystals of Ba₈Al₁₆Ge₃₀, Ba₈Ga₁₆Ge₃₀, Sr₈Ga₁₆Ge₃₀, silicon, and germanium as standard references. The effective mass, Hall carrier mobility, and lattice thermal conductivity, which govern the transport properties, are determined to be ~ 2.4m ₀, ~ 7 cm² V^?1 s^?1, and ~ 1.3 W m^?1 K^?1, respectively, for actual Al content x of about 14.77. The thermoelectric figure of merit ZT is estimated to be about 0.35 at 900 K for actual Al content x of about 14.77.     

3‐Level Envelope Delta‐Sigma Modulation RF Signal Generator for High‐Efficiency Transmitters

This paper presents a 0.13 μm CMOS 3‐level envelope delta‐sigma modulation (EDSM) RF signal generator, which synthesizes a 2.6 GHz‐centered fully symmetrical 3‐level EDSM signal for high‐efficiency power amplifier architectures. It consists of an I‐Q phase modulator, a Class B wideband buffer, an up‐conversion mixer, a D2S, and a Class AB wideband drive amplifier. To preserve fast phase transition in the 3‐state envelope level, the wideband buffer has an RLC load and the driver amplifier uses a second‐order BPF as its load to provide enough bandwidth. To achieve an accurate 3‐state envelope level in the up‐mixer output, the LO bias level is optimized. The I‐Q phase modulator adopts a modified quadrature passive mixer topology and mitigates the I‐Q crosstalk problem using a 50% duty cycle in LO clocks. The fabricated chip provides an average output power of –1.5 dBm and an error vector magnitude (EVM) of 3.89% for 3GPP LTE 64 QAM input signals with a channel bandwidth of 10/20 MHz, as well as consuming 60 mW for both channels from a 1.2 V/2.5 V supply voltage.     

Extraction of interface states at emitter–base heterojunctions in AlGaAs/GaAs heterostructure bipolar transistors using sub-bandgap photonic excitation

Distribution of interface states at the emitter–base heterojunctions in heterostructure bipolar transistors (HBTs) is characterized by using current–voltage characteristics using sub-bandgap photonic excitation. Sub-bandgap photonic source with a photon energy E_ph which is less than the energy bandgap E_g (E_g,GaAs = 1.42, E_g,AlGaAs = 1.76 eV) of emitter, base, and collector of HBTs, is employed for exclusive excitation of carriers only from the interface states in the photo-responsive energy range at emitter–base heterointerface. The proposed method is applied to an Al_0.3Ga_0.7As/GaAs HBT (A_E = W_E × L_E = 250 × 100 μm²) with E_ph = 0.943 eV and P_opt = 3 mW. Extracted interface trap density D_it was observed to be D_it,max  4.2 × 10¹² eV⁻¹ cm⁻² at emitter–base heterointerface.     

Recent Progress in Applications of the Cold Sintering Process for Ceramic–Polymer Composites

Ceramic–polymer composites are of interest for designing enhanced and unique properties. However, the processing temperature windows of sintering ceramics are much higher than that of compaction, extrusion, or sintering of polymers, and thus traditionally there has been an inability to cosinter ceramic–polymer composites in a single step with high amounts of ceramics. The cold sintering process is a low‐temperature sintering technology recently developed for ceramics and ceramic‐based composites. A wide variety of ceramic materials have now been demonstrated to be densified under the cold sintering process and therefore can be all cosintered with polymers from room temperature to 300 °C. Here, the status, understanding, and application of cold cosintering, with different examples of ceramics and polymers, are discussed. One has to note that these types of cold sintering processes are yet new, and a full understanding will only emerge after more ceramic–polymer examples emerge and different research groups build upon these early observations. The general processing, property designs, and an outlook on cold sintering composites are outlined. Ultimately, the cold sintering process could open up a new multimaterial design space and impact the field of ceramic–polymer composites.     

Electrical and Thermal Conductivity and Conduction Mechanism of Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript> Alloy

Ge₂Sb₂Te₅ alloy has drawn much attention due to its application in phase-change random-access memory and potential as a thermoelectric material. Electrical and thermal conductivity are important material properties in both applications. The aim of this work is to investigate the temperature dependence of the electrical and thermal conductivity of Ge₂Sb₂Te₅ alloy and discuss the thermal conduction mechanism. The electrical resistivity and thermal conductivity of Ge₂Sb₂Te₅ alloy were measured from room temperature to 823 K by four-terminal and hot-strip method, respectively. With increasing temperature, the electrical resistivity increased while the thermal conductivity first decreased up to about 600 K then increased. The electronic component of the thermal conductivity was calculated from the Wiedemann–Franz law using the resistivity results. At room temperature, Ge₂Sb₂Te₅ alloy has large electronic thermal conductivity and low lattice thermal conductivity. Bipolar diffusion contributes more to the thermal conductivity with increasing temperature. The special crystallographic structure of Ge₂Sb₂Te₅ alloy accounts for the thermal conduction mechanism.     

Neuro-Glia-Vascular-on-a-Chip System to Assess Aggravated Neurodegeneration via Brain Endothelial Cells upon Exposure to Diesel Exhaust Particles

Air pollution induces neurodegeneration, including cognitive deficits, neuroinflammation, and disruption of the blood–brain barrier. The mechanisms underlying air pollution-mediated neurodegeneration have not yet been fully elucidated given the limited knowledge on intercellular interactions. A brain-on-a-chip platform is presented comprising neurons, glia, and brain endothelial cells (bECs; neuro-glia-vascular, NGV) and diesel exhaust particle (DEP)-induced neurodegeneration is evaluated with a particular focus on the intercellular interactions. DEP exposure in the NGV model yields Alzheimer's disease-like signatures, including amyloid beta accumulation, tau phosphorylation, hydrogen peroxide (H₂O₂)/reactive oxygen species (ROS) production, and neuronal cell death. bEC-secreted granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates microglial activation and the overproduction of H₂O₂/ROS in microglia, suggesting that the bEC-microglia-neuron is a neurodegeneration cascade. Pharmacological inhibition at each step of the cascade, including GM-CSF neutralization, microglial activation suppression, and ROS scavenging, prohibits neurodegeneration in the NGV model. Therefore, intercellular interactions should be further studied of air pollution-induced neurodegeneration.     

Organic Phenolic Configurationally Locked Polyene Single Crystals for Electro‐optic and Terahertz Wave Applications

We investigate a configurationally locked polyene (CLP) crystal 2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor. The OH1 crystals with orthorhombic space group Pna2₁ (point group mm2) exhibit large second‐order nonlinear optical figures of merit, high thermal stability and very favorable crystal growth characteristics. Higher solubility in methanol and a larger temperature difference between the melting temperature and the decomposition temperature of OH1 compared to analogous CLP crystals, are of advantage for solution and melt crystal growth, respectively. Acentric bulk OH1 crystals of large sizes with side lengths of up to 1 cm with excellent optical quality have been successfully grown from methanol solution. The microscopic and macroscopic nonlinearities of the OH1 crystals are investigated theoretically and experimentally. The OH1 crystals exhibit a large macroscopic nonlinearity with four times larger powder second harmonic generation efficiency than that of analogous CLP crystals containing dimethylamino electron donor. A very high potential of OH1 crystals for broadband THz wave emitters in the full frequency range of 0.1–3 THz by optical rectification of 160 fs pulses has been demonstrated.