Enhanced Electrochromism with Rapid Growth Layer‐by‐Layer Assembly of Polyelectrolyte Complexes

In this work, a facile method to deposit fast growing electrochromic multilayer films with enhanced electrochemical properties using layer‐by‐layer (LbL) self‐assembly of complex polyelectrolyte is demonstrated. Two linear polymers, poly(acrylic acid) (PAA) and polyethylenimine (PEI), are used to formulate stable complexes under specific pH to prepare polyaniline (PANI)/PAA‐PEI multilayer films via LbL deposition. By introducing polymeric complexes as building blocks, [PANI/PAA‐PEI]_n films grow much faster compared with [PANI/PAA]_n films, which are deposited under the same condition. Unlike the compact [PANI/PAA]_n films, [PANI/PAA‐PEI]_n films exhibit porous structure that is beneficial to the electrochemical process and leads to improved electrochromic properties. An enhanced optical modulation of 30% is achieved with [PANI/PAA‐PEI]₃₀ films at 630 nm compared with the lower optical modulation of 11% measured from [PANI/PAA]₃₀ films. The switching time of [PANI/PAA‐PEI]₃₀ films is only half of that of [PANI/PAA]₃₀ films, which indicates a faster redox process. Utilizing polyelectrolyte complexes as building blocks is a promising approach to prepare fast growing LbL films for high performance electrochemical device applications.     

Theoretical design for 120 GHz semiconductor junction circulators: effects of different numbers of terms in the Green's function

A theoretical analysis of the predicted performance and field distributions for semiconductor junction circulators is based on Bosma's Green's function approach which involves a summation of infinite series in the mathematical derivation. The effects are considered of taking a different number of terms in the series, looking at three different circulators centred at 120 GHz. The narrowband semiconductor circulators show a similar effect to the ferrite junction circulator because the field distributions inside the semiconductor discs can be approximated by only considering the dominant modes. However, there is no dominant mode in the broadband circulator and the higher order modes play an important role in the operation of this circulator. In order to obtain a precise representation of the circulation effects inside both narrowband and broadband circulators, at least up to the 6th term, or 18 terms in all, are required to be added in the summation of Green's functions.     

Hydrodynamically Guided Hierarchical Self‐Assembly of Peptide–Protein Bioinks

Effective integration of molecular self‐assembly and additive manufacturing would provide a technological leap in bioprinting. This article reports on a biofabrication system based on the hydrodynamically guided co‐assembly of peptide amphiphiles (PAs) with naturally occurring biomolecules and proteins to generate hierarchical constructs with tuneable molecular composition and structural control. The system takes advantage of droplet‐on‐demand inkjet printing to exploit interfacial fluid forces and guide molecular self‐assembly into aligned or disordered nanofibers, hydrogel structures of different geometries and sizes, surface topographies, and higher‐ordered constructs bound by molecular diffusion. PAs are designed to co‐assemble during printing in cell diluent conditions with a range of extracellular matrix (ECM) proteins and biomolecules including fibronectin, collagen, keratin, elastin‐like proteins, and hyaluronic acid. Using combinations of these molecules, NIH‐3T3 and adipose derived stem cells are bioprinted within complex structures while exhibiting high cell viability (>88%). By integrating self‐assembly with 3D‐bioprinting, the study introduces a novel biofabrication platform capable of encapsulating and spatially distributing multiple cell types within tuneable pericellular environments. In this way, the work demonstrates the potential of the approach to generate complex bioactive scaffolds for applications such as tissue engineering, in vitro models, and drug screening.     

Study on stacking faults and microtwins in wide bandgap II-VI semiconductor heterostructures grown on GaAs

ZnMgSSe and ZnSSe layers grown on GaAs substrates with GaAs buffer layers by molecular beam epitaxy have been examined by transmission electron microscopy (TEM). The depth level at which paired triangular stacking faults are nucleated in the ZnMgSSe/GaAs heterostructure has been investigated by using the plan-view TEM technique. It has been found that in the ZnMgSSe/GaAs heterostructure the nucleation of the paired stacking faults occurs within a range of depth which starts at the II-VI/GaAs interface and ends at a level that is above the interface by about 120 nm. The dominant type of defects in ZnSSe layers, which have the single triangular shape, has been identified to be microtwins by high resolution TEM.     

Effects of high temperature annealing on the device characteristics of Ga0.52In0.48P/GaAs and Al0.52In0.48P/GaAs heterojunction bipolar transistors

GaInP/GaAs and AlInP/GaAs heterojunction bipolar transistor (HBT) structures were grown by low pressure metalorganic vapor phase epitaxy and annealed at various temperatures up to 675°C for 15 min. Subsequent comparisons with HBTs fabricated on both annealed and unannealed control samples showed no effects for annealing up to and including 575°C, but significant changes in the electrical characteristics were observed at an annealing temperature of 675°C. For the GaInP/GaAs devices, the base current increased by a significant amount, reducing the gain and increasing the base current ideality factor from 1.07 to 1.9. Photoluminescence and electrical measurements on the structures indicated that both the emitter and base were affected by an increase in the recombination times in those regions. These effects were attributed to an out-diffusion of hydrogen from the base during annealing. The emitter of the AlInP/GaAs HBT was affected less by the hydrogen diffusion because of the larger bandgap. These observations have important implications for device performance dependence on the details of the temperature/time profile subsequent to the base growth.     

In vivo Doppler shift measurements using multimode fiber-opticcatheters

A new fiber-optic catheter for in vivo blood-flow measurements has been developed. The catheter is designed to measure blood flow in both the forward (toward the catheter tip) and reverse (away from the catheter tip) flow directions. It consists of two multimode optical fibers with core diameter of 50 μm and cladding diameter of 125 μm. One fiber transmits the laser beam into blood and the other receives the backscattered light from the erythrocytes within the probe volume. In the flow experiment, it was found that the flow within the boundary layer is indeed laminar and, hence, the relationship between the Doppler shift frequencies and the flow velocities is linear, thereby making the linear calibration possible for predicting the free stream flow velocity. Plots of the maximum shift frequency (frequency at which the Doppler spectrum disappeared into the noise spectrum) against the flow velocities are found to be more linear in both the forward and reverse flow directions than that of the dominant shift frequency (frequency with the highest amplitude). These results were reaffirmed by the numerical flow simulation along the catheter side wall     

Scalar quantisation of LSF parameters using vector measurement

A new form of line spectral frequency (LSF), bounded line spectral frequency, is presented. It is shown that the new representation is more efficient than the direct line spectral frequency and the differential line spectral frequency (DLSF). By using a vector measure, the scalar quantisation of tenth-order linear predictive coding (LPC) parameters can be coded at 28 bit/frame with a transparent quantisation quality     

Performance evaluation of the recuperative heat exchanger in a miniature Joule–Thomson cooler

To develop effective heat exchangers for miniature and micro-Joule–Thomson (J–T) cooling system, the performance of the recuperative heat exchanger in a miniature J–T cooler is analyzed and evaluated. The evaluation is based on a theoretical model of the Hampson-type counter-flow heat exchanger. The effect of the pressure and temperature-dependent properties and longitudinal heat conduction are considered. The results of the numerical simulation are validated with the corresponding experimental measurements. The performance of the heat exchanger on effectiveness, flow and various heat conduction losses as well as liquefied yield fraction are analyzed and discussed. The simulation model provides a useful tool for miniature J–T cooler design.     

Bright Aggregation‐Induced Emission Dots for Dynamic Tracking and Grading of Patient‐Derived Xenografts in Zebrafish

Cancer prognosis will benefit from a scoring system that could grade malignant traits of patient‐derived cells by assessing their growth and metastasis in a living system. Specific tracking of patient‐derived cells requires labeling by contrast agents with good signal‐to‐noise ratio and no specific stain of host tissues. Towards this aim, aggregation‐induced emission (AIE) dots are developed for in vivo cancer tracking with emphasis on reproducible optimized formulation and specific fluorescent labeling of cells that enable enhanced spatial temporal resolution in vivo. The importance of energy‐dependent AIE dots uptake for patient‐derived cell labeling is emphasized to reveal their specific uptake by viable cancer cells. Using optically transparent zebrafish embryo, the ability is demonstrated to follow the engraftment of transplanted AIE dot labeled cells in zebrafish brains over one week. Cells detected outside the brain after 7 d are quantified as metastatic cells. Results from seven clinical samples demonstrate the utility of this methodology to differentiate low engraftment level of benign neoplasms from higher engraftment level and metastasis detected in malignant ovarian cancer specimens. Achieving clinically validated results supports the use of AIE dot labeled patient derived cells in zebrafish xenografts for future cancer prognosis.     

The slot-coupled hemispherical dielectric resonator antenna with a parasitic patch: applications to the circularly polarized antenna and wide-band antenna

The aperture-coupled hemispherical dielectric resonator antenna (DRA) with a parasitic patch is studied rigorously. Using the Green's function approach, integral equations for the unknown patch and slot currents are formulated and solved using the method of moments. The theory is utilized to design a circularly polarized (CP) DRA and a wide-band linearly polarized (LP) DRA. In the former, the CP frequency and axial ratio (AR) can easily be controlled by the patch location and patch size, respectively, with the impedance matched by varying the slot length and microstrip stub length. It is important that the AR will not be affected when the input impedance is tuned, and the CP design is therefore greatly facilitated. For the wide-band LP antenna, a maximum bandwidth of 22% can be obtained, which is much wider than the previous bandwidth of 7.5% with no parasitic patches. Finally, the frequency-tuning characteristics of the proposed antenna are discussed. Since the parasitic patch can be applied to any DRAs, the method will find applications in practical DRA designs.