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The poor conductivity and deficient active sites of transition metal oxides lead to low energy density of supercapacitors, which limits their wide application. In this work, double transition metal oxide heterojunctions with oxygen vacancy (Vo-ZnO/CoO) nanowires are prepared by effective hydrothermal and thermal treatments. The formation of the heterojunction results in the redistribution of interface charge between ZnO and CoO, generating an internal electric field to accelerate the electron transport. Meanwhile, oxygen vacancies can enhance the redox reaction activity to further improve the electrochemical kinetics of the electrode material. Therefore, the prepared Vo-ZnO/CoO can provide a superior specific capacity of 845 C g−1 (1 A g−1). An asymmetric supercapacitor with the Vo-ZnO/CoO as positive electrode shows a higher energy density of 51.6 Wh kg−1 when the power density reaches 799.9 W kg−1. This work proposes a synergistic combination of defect and heterojunction engineering to improve the electrochemical properties of materials, providing an important guidance for material design in energy-storage field.

In our previous work, the detailed crystal structure, optical and electrical properties of evaporated CdS (hexagonal CdS) and chemical bath deposition CdS (cubic CdS) were discussed. The hexagonal CdS film is more suitable as the buffer layer for Sb2Se3 film solar cells compared with its cubic counterpart. However, in our experiments, the influence of high annealing temperature on hexagonal CdS is difficult to control. Moreover, hexagonal CdS is unsuitable for large-area industrial production of Sb2Se3 solar cells. In this study, an electron beam evaporation-prepared CdS buffer layer (hexagonal CdS) with high quality, uniformity and low-temperature treatment was introduced in Sb2Se3 thin film solar cells. The influence of different substrate temperatures during electron beam evaporation on the crystal structure, surface morphologies, and optical properties of CdS and Sb2Se3 films was investigated. The device performance improvement from 3.52% to 5.89% was obtained after the surface roughness of the CdS film and the heterojunction interface were optimised. Lastly, the efficiency of the Sb2Se3 solar cells was obtained to be 6.71% based on the structure of FTO/EB-CdS/Sb2Se3/MoO3/Au.

Background: Distant metastasis is the major cause of treatment failure in locally advanced rectal cancer (LARC). Adjuvant chemotherapy (AC) is usually used for distant control. However, only certain subgroups of patients could benefit from AC. Our aim was to develop a radiomics model for the prediction of survival and chemotherapeutic benefits using pretreatment multiparameter MR images and clinicopathological features in patients with LARC. Methods: 186 consecutive patients with LARC underwent feature extraction from the whole tumor on T2-weighted (T2w), contrast enhanced T1-weighted (cT1w), and ADC images. Feature selection was based on feature stability and the Boruta algorithm. Radiomics signatures for predicting DFS (disease-free survival) were then generated using the selected features. Combining clinical risk factors, a radiomics nomogram was constructed using Cox proportional hazards regression model. The predictive performance was evaluated by Harrell's concordance indices (C-index) and time-independent receiver operating characteristic (ROC) analysis. Results: Four features were selected to construct the radiomics signature, which was significantly associated with DFS (P < 0.001). The radiomics nomogram, incorporating radiomics signature and two clinicopathological variables (pN and tumor differentiation), exhibited better prediction performance for DFS than the clinicopathological model, with C-index of 0.780 (95%CI, 0.718-0.843) and 0.803 (95%CI, 0.717-0.889) in the training and validation cohorts, respectively. The radiomics nomogram-defined high-risk group had a shorter DFS, DMFS, and OS than those in the low-risk group (all P Conclusion: This study demonstrated that the newly developed pretreatment multiparameter MRI-based radiomics model could serve as a powerful predictor of prognosis, and may act as a potential indicator for guiding AC in patients with LARC.

For structures with both random and fuzzy uncertainty, this paper presents a novel method for determining the membership function in fuzzy reliability with the Automatic Updating Extreme Response Surface (AUERS) method. In the proposed method, fuzzy variables are initially converted into a value domain under the given cut level and the extreme point in the domain where the reliability reaches its extreme value is considered. Second, the Particle Swarm Optimization (PSO) algorithm is used to determine the extreme point according to the extreme responses for different sets of random sample inputs. A kriging response surface is subsequently constructed between the random variables and the corresponding extreme points. An automatic updating strategy is then introduced based on the Relative Mean Square Predicted Error (RMSPE) before performing every iteration of reliability analysis. By adding new sample points, the approximate quality of the kriging response surface is improved. Finally, reliability analysis is used to determine the reliability bound under the given cut level. The proposed method assures the accuracy and computation efficiency of the mixed uncertainty reliability analysis results while it prevents the solution from becoming trapped in a local optimum, which occurs in classical optimization methods. Two example analyses are used to demonstrate the validity and advantages of the proposed method.

Respiration is an important physiological process of human body that can not only act as vital signs for physical health management or “biomarkers” of some diseases, but also as a kind of energy that can be utilized to drive triboelectric nanogenerator (TENG). It is particularly desirable to develop a facile TENG that can be driven by human respiration itself for multifunctional human respiratory monitoring. In this work, a respiration-driven TENG based on Ce-doped ZnO-PANI nanocomposite film that can convert respiratory airflow energy into electric signals was developed for the detection of multiple respiratory parameters including trace-level NH3 concentration, human respiratory flow and respiratory frequency. It was found that the as-designed TENG exhibited excellent ability for respiratory flow monitoring (2–6 L/min), identification of human breathing frequency and recognition of different breathing patterns. Furthermore, output voltage of the self-powered NH3 sensor monotonously decreases with the increase of NH3 concentrations from 0.1 to 25 ppm. Especially, a good NH3-sensing performance was exhibited when exposed to a trace-level NH3 atmosphere ranging from 0.1 to 1 ppm, implying a promising potential in self-powered disease screening related to the detection of exhaled NH3 in human breathing. This research offers a facile method to establish a multifunctional respiratory monitoring system driven by respiration itself, which is of significant importance in self-powered human health monitoring through non-implantable respiratory diagnosis.

Biofouling has been a long-last problem in a variety of marine systems which causes energy waste and device damage. In this study, we present a self-activated anti-biofouling system enabled by electrical double layer disturbance, which could effectively suppress the initial formation of conditioning layers and subsequent microbe attachment. The small and low-frequency alternating electrical fields were produced by a triboelectric nanogenerator under water wave impacts. Systematic analyses confirmed that the anti-biofouling efficacy was directly related to the strength of the electric field and was effective in both fresh lake and sea water environments. An on-site demonstration was implemented at a calm lake shore for three weeks. The water wave-driven anti-biofouling exhibited excellent surface protection, which was significantly superior to several commercial anti-biofouling coatings. This development brings a novel, effective and eco-friendly solution for protecting a broad range of surfaces against biofouling.

Volatile organic sulfur compounds (VOSCs) pose serious threats to environment and human health, while detection techniques of VOSCs are expensive and complex. Here, this paper first-time reported a hydrogen-bond acidic (HBA) polymer-based surface acoustic wave (SAW) chemical sensor for the detection of four VOSCs (methyl mercaptan, dimethyl sulfide, dimethyl disulfide, and carbon disulfide). The results show that this sensor exhibited both excellent sensitivity (limit of detections ranging from 0.035 to 0.11 mg/m3) with fast response and recovery and high selectivity (2.23–49.6 times higher response than interference vapors) toward VOSCs at room temperature. The good performance is attributed to the hydrogen bonding between the sulfur atom of VOSCs and hydrogen atom of hexafluoroisopropanol (HFIP) groups in polymer chain. Fourier-transform infrared spectroscopy (FTIR) spectrum and first principle calculations were performed to further support this proposed mechanism.

Aerodynamic inverse design is proposed using multifidelity models and the manifold mapping (MM) technique. Aerodynamic inverse design aims at achieving a target performance characteristic, such as a pressure coefficient distribution of an airfoil or local lift distribution of a wing. Due to the high computational cost of accurate aerodynamic models and the large number of design variables, the overall cost of inverse design can be prohibitive. The MM-based optimization algorithm leverages the speed of the low-fidelity model to accelerate the optimization process, but refers back to the high-fidelity model to ensure an accurate solution. In this work, the MM technique is applied to the characteristic distribution under consideration in each application. In particular, the pressure coefficient distribution is modeled with the MM technique in the case of airfoil inverse design, and the sectional lift distribution in the case of wing design. The proposed method is tested and evaluated on six airfoil inverse design cases and one rectangular wing inverse design case. In the two-dimensional cases, parameterized with eight design variables, direct aerodynamic inverse design using pattern search required 700 to 1200 high-fidelity model evaluations, which took 300 to 700 hours in total. The MM-based design algorithm required less than 20 high-fidelity simulations and 1000 to 2000 low-fidelity evaluations, which took 30 to 90 hours. In the three-dimensional case, parameterized with three design variables, direct aerodynamic inverse design took around 50 hours, whereas the MM-based design needed around six hours.

An ultrasensitive self-powered ammonia (NH3) sensing system based on a vertical contact-separate mode triboelectric nanogenerator (TENG) has been proposed for room temperature detection of NH3 concentrations both in the ambient environment and in human exhaled gases. Owing to the special output characteristics of the TENG adjusted by the load resistance of the NH3 sensor, output voltage of the fabricated gas sensor has a proportional relationship with NH3 concentration, which is the fundamental working mechanism of the self-powered gas-sensing system. The triboelectric ammonia sensor (TEAS) based on PANI-MWCNTs composite thin film possesses a NH3-sensing response of 10% at 0.01 ppm NH3 and exhibits a great response of 255% at 100 ppm NH3. Meanwhile, the TEAS also holds fast response/recovery time (89–120 s/103–127 s for 0.6–100 ppm NH3), excellent long-term stability, satisfactory selectivity and good anti-bending ability. Furthermore, a preliminary test of human exhaled NH3 concentration has been carried out to further expand the practical application of the developed TEAS. The results not only provide an effective technique in ultrasensitive NH3 sensing but also greatly broaden the applicability of TENG in the detection of human kidney health through comparing to average NH3 concentrations within exhaled gases of healthy people.

Fully transparent electronics are of increasing interest for biological applications, where the combination of sensing and imaging can potentially improve patient healthcare diagnostics. Herein, we report high-performance, fully-transparent amorphous In-Ga-Zn-O field-effect transistor (a-IGZO FET) based biosensors fabricated directly on highly-curved glass substrates. The a-IGZO channel and indium tin oxide electrodes were patterned directly on glass tubes (1.0 mm radius) by microcontact printing self-assembled monolayers and etching the metal oxide films. This approach led to a-IGZO FETs with excellent electronic performance, with high on/off drain current ∼1.3 × 106, high average electron mobility > 7.4 cm2/Vs, low on/off hysteresis ∼0.6, V and low gate leakage current ∼10−10 A. The back-channel of the a-IGZO FETs were functionalized with glucose oxidase to make fully transparent biosensors with very high sensitivity to glucose. We have determined that the glucose limit of detection is 170 μM. These results provide insight into new methods for fabricating a-IGZO FETs and a-IGZO FET biosensors on non-planar substrates, and may open a range of new applications, including transparent sensing catheters, flexible active transparent electrode sensing arrays, and integration of FET based biosensors on optical fibers.

The triboelectric nanogenerator (TENG) driven self-powered gas sensor has been developed for room temperature nitrogen dioxide (NO2) detection under UV illumination (365 nm). Powered by TENG, the concentration of NO2 can be spontaneously detected via chemoresistive gas sensor based on Zinc Oxide-Reduced graphene oxide (ZnO-RGO) hybrid films, where the voltage drop across the interdigital electrodes (IDEs) has a proportional relationship with NO2 concentration. The self-powered triboelectric gas sensor (TGS) composed by ZnO-RGO composite films exhibit superior response (~ 16.8) and sensitivity as well as selectivity than that for pure ZnO film. With respect to selectivity, the response of ZnO-RGO composite film based TGS to NO2 was at least 49-fold higher than those for other gases. Furthermore, through a signal processing circuit, a self-powered NO2 gas alert system was developed for real-time monitoring the ambient NO2 concentration. This work not only promotes the applicability of TENGs as self-powered sensors but also pushes forwards the active sensing network node for environmental monitoring by harvesting ambient energy.

A resistive-type flexible ammonia (NH3) sensor was proposed and developed in this work, which was prepared by depositing polyaniline-cerium dioxide (PANI-CeO2) nanocomposite thin film on flexible polyimide (PI) substrate through in-situ self-assembly method. The effect of CeO2 nanoparticles on the polymerization of aniline was studied by comparing the morphological, structural and chemical features of the pure PANI and PANI-CeO2 nanocomposite, and the dynamic polymerization processes were also recorded and investigated. In this process, an interesting phenomenon was found that the protonation and oxidation degrees of PANI in PANI-CeO2 nanocomposite were improved significantly according to the XPS spectra analysis, which should be ascribed to the synergetic oxidation of CeO2 nanoparticles and ammonium persulfate (APS). Meanwhile, the NH3-sensing performances of the pure PANI and PANI-CeO2 film sensors were evaluated at room temperature (∼25 °C), which showed that the PANI-CeO2 film sensor possessed enhanced response, reduced recovery time, perfect response-concentration linearity, good reproducibility, splendid selectivity, remarkable long-term stability, ultra-low detectable concentration (16 ppb) and theoretical detection limit (0.274 ppb), and outstanding flexibility without significant response decrease after 500 bending/extending cycles. It was speculated that the excellent sensing performances should probably benefit from the gas-sensing enhancement effect of p-n junction, the improved protonation degree and modified morphology of PANI by the addiction of CeO2 nanoparticles. And, the high flexibility might originate from the flexible structure of PANI chains, and the good adhesion and nano-mechanical performance of PANI-CeO2 film. Besides, the effect of relative humidity on the sensing properties of PANI-CeO2 film sensor was also discussed and analyzed. Therefore, the proposed high-performance flexible PANI-CeO2 thin film sensor holds great promise for application into hand-held or wearable electronic devices for trace-level NH3 detection at room temperature.

Functional and structural tailoring of three-dimensional (3D) conducting polymer nanoarchitectures is a promising route but remains challenging to develop high-performance electrodes for electrochemical energy storage. Herein, we design poly(3, 4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) 3D mesoporous aerogel electrodes through a simple and original one-pot mechanochemical processing route. The hierarchical structure of neat PEDOT:PSS aerogels displays a highly interpenetrated porous conductive network with a record high active surface area of 470 m 2 g −1 amongst the class of conducting polymer architectures. Robust structural and electrochemical performances are achieved with high gravimetric, areal and volumetric capacitance metrics of 120 F/g, 2.5 F cm −2 , and 124 F cm −3 , respectively, as the result of a mixed hybrid faradaic - capacitive charge storage mechanism. Moreover, these performances are attained in organic based electrolytes, reported so far to be incompatible or hinder the electrochemical activity of PEDOT:PSS. We undermine the fundamentals of the electrochemical operation in these electrodes and show that the electrolyte chemistry and the aerogel morphology particularly impact the charge storage performances demonstrating the superiority of the mesoporous architecture for charge transfer and ion exchange. Asymmetric cells are built having a specific capacitance of 40 F/g based on the total mass of electrodes and a good cyclic stability with 90% capacitance retention after 1000 charge and discharge cycles. This study offers a new route to enhance the electrochemical properties of conducting polymers and provides suggestive insights for developing high-performance polymer electrode materials for electrochemical energy storage.

In this work, a fundamental new approach for humidity detection was proposed. By coupling triboelectric nanogenerator (TENG) with resistive humidity sensor, the degree of ambient moisture can be actively detected at room temperature, where the voltage drops across the interdigital electrodes (IDEs) has a reversely proportional relationship with relative humidity. The prepared self-powered triboelectric humidity sensor (THS) holds high humidity response of ∼7, fast response/recovery time of 2.8 s and 3.5 s, stable repeatability and excellent long term stability. With respect to selectivity, the response of THS to gaseous water was at least 2-fold higher than those for other gases. Furthermore, through a signal processing circuit, a self-powered humidity alert system was developed for real-time monitoring the ambient humidity. Finally, the underlying working principle of the proposed sensor was discussed in detail. This research not only provides a simple, low-cost and efficient means in humidity sensing but also greatly broadens the applicability of TENGs as self-powered active sensors.

Aerodynamic optimization based on computational fluid dynamics (CFD) is a powerful design approach because it significantly reduces the design time compared with the human manual design. However, CFD-based optimization can still take hours to converge because it requires repeatedly running computationally expensive flow simulations. To further shorten the design optimization time, we propose a fast, interactive design framework that allows us to complete an airfoil aerodynamic optimization within a few seconds. This framework is made efficient through a B-spline-based generative adversarial network model for shape parameterization, which filters out unrealistic airfoils for a reduced design space that contains all relevant airfoil shapes. Moreover, we use a combination of multilayer perceptron, recurrent neural networks, and mixture of experts for surrogate modeling to enable both scalar (drag and lift) and vector (pressure distribution) response predictions for a wide range of Mach numbers (0.3 to 0.7) and Reynolds numbers (104 to 1010). To verify our proposed framework, we compare the optimization results with the ones computed by direct CFD-based optimization for subsonic and transonic conditions. The results show that the optimal designs and the aerodynamic quantities (lift, drag, and pressure distribution) obtained by our proposed framework agree well with the ones computed by direct CFD-based optimizations and evaluations. The proposed framework is being integrated into a web-based interactive aerodynamic design framework that allows users to predict drag, lift, moment, pressure distribution, and optimal airfoil shapes for a wide range of flow conditions within seconds.

According to the theory of a gas chromatography column, the air flow distribution inside the channel plays a vital role in the peak broadening. Unlike the semi-packed columns which utilized embedded posts to obtain a more uniform lateral distribution compared to the open tubular columns, this paper reports the design and fabrication of a MEMS-based GC column folded in a wavy configuration to achieve an even flow velocity. The wavy column consists of upper arcs and lower arcs which are alternatively connected in series. The flow distributions of wavy columns with various arc angle and curvature radius are explored by the finite element method. The simulation reveals that the average flow velocity decreases with the increase of the arc angle, resulting in a successive improvement of the flow uniformity at the zones between two adjacent bends but also a more nonsymmetric distribution at the bends. These two effects counteract with each other and render an optimal arc angle of 136°. To verify the above design, the 136° wavy column and a serpentine column with the same dimensions are compared, where a better separation performance of the wavy column is demonstrated.

Fast and accurate airfoil design under uncertainty using non-intrusive polynomial chaos (NIPC) expansions and utility functions is proposed. The NIPC expansions provide a means to efficiently and accurately compute statistical information for a given set of input variables with associated probability distribution. Utility functions provide a way to rigorously formulate the design problem. In this work, these two methods are integrated for the design of airfoil shapes under uncertainty. The proposed approach is illustrated on a numerical example of lift-constrained airfoil drag minimization in transonic viscous flow using the Mach number as an uncertain variable. The results show that compared with the standard problem formulation the proposed approach yields more robust designs. In other words, the designs obtained by the proposed approach are less sensitive to variations in the uncertain variables than those obtained with the standard problem formulation.

In this paper, we discuss a computationally efficient approach to expedite design optimization of broadband hybrid couplers occupying a minimized substrate area. Structure size reduction is achieved here by decomposing an original coupler circuit into low- and high-impedance components and replacing them with electrically equivalent slow-wave lines with reduced physical dimensions. The main challenge is reliable design of computationally demanding low-impedance slow-wave structures that feature a quasi-periodic circuit topology for wideband operation. Our goal is to determine an adequate number of recurrent unit elements as well as to adjust their designable parameters so that the coupler footprint area is minimal. The proposed method involves using surrogate-based optimization with a reconfigurable co-simulation coarse model as the key component enabling design process acceleration. The latter model is composed in Keysight ADS circuit simulator from multiple EM-evaluated data blocks of the slow-wave unit element and theory-based feeding line models. The embedded optimization algorithm is a trust-region-based gradient search with coarse model Jacobian estimation. We exploit a penalty function approach to ensure that the electrical conditions for the slow-wave lines are accordingly satisfied, apart from explicitly minimizing the area of the coupler. The effectiveness of the proposed technique is demonstrated through a design example of two-section 3-dB branch-line coupler. For the given example, we obtain nine circuit design solutions that correspond to the compact couplers whose multi-element slow-wave lines are composed of unit cells ranging from two to ten.

A deterministic technique for fast surrogate-assisted multi-objective design optimization of antennas in highly-dimensional parameters spaces has been discussed. In this two-stage approach, the initial approximation of the Pareto set representing the best compromise between conflicting objectives is obtained using a bisection algorithm which finds new Pareto-optimal designs by dividing the line segments interconnecting previously found optimal points, and executing poll-type search that involves Pareto ranking. The initial Pareto front is generated at the level of the coarsely-discretized EM model of the antenna. In the second stage of the algorithm, the high-fidelity Pareto designs are obtained through optimization of corrected local-approximation models. The considered optimization method is verified using a 17-variable uniplanar antenna operating in ultra-wideband frequency range. The method is compared to three state-of-the-art surrogate-assisted multi-objective optimization algorithms.

In this work, a novel graphene oxide (GO)/Poly(ethyleneimine) (PEI) layered film was designed and prepared on quartz crystal microbalance (QCM) for humidity detection through a feasible spray process at room temperature. The morphological and chemical properties of GO/PEI layered film were examined by means of field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared spectroscopy (FTIR), and Raman spectroscopy. The effect of GO solution concentration on humidity-sensing characteristics was investigated and an optimized QCM humidity sensor was obtained. An intriguing phenomenon was observed that a three-dimension structure of GO sheets was formed due to the redissolution effect at the interface between PEI and GO layers. Results showed that a layered film QCM sensor exhibited superior humidity sensing properties than a pure GO film or a PEI one including high response, short response/recovery time, small humidity hysteresis (less than 1%RH), excellent repeatability, selectivity and long-term stability. Moreover, the humidity features of sensors were also researched via the method of impedance analysis. Lastly, a convincing sensing mechanism model was established to interpret the enhanced humidity-sensing performance of layered film sensors. The results demonstrated the potential application of GO/PEI layered films to humidity sensors.

In this paper, a protonated polyethylenimine (P-PEI)-graphene oxide (GO) nanocomposite thin film, referred as P-PEI-GO, was deposited on the quartz crystal microbalance (QCM) by a facile dipping process for the development of high performance humidity sensors. The morphological and structural characteristics of P-PEI-GO thin film were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscope. The humidity-sensing properties, such as response and recovery, sensitivity, repeatability, selectivity, humidity hysteresis and long-term stability, were investigated in a wide range of working humidity (11–97% RH). The resultant P-PEI-GO nanocomposite thin film possesses much larger specific surface area and richer hydrophilic groups than pure P-PEI film, leading to higher sensitivities and shorter response/recovery times of the sensor. Especially, the sensor preserves excellent durability, small hysteresis, good selectivity and stability compared with individual P-PEI or GO film sensor, which could be ascribed to the high mechanical modulus of GO and weak interaction between P-PEI and GO. Finally, the humidity sensing mechanism of proposed sensor was discussed in details. This research provides a feasible and effective approach to construct high performance humidity sensor operated at room temperature based on GO nanocomposites.

A single-electrode-based segmented triboelectric nanogenerator (S-TENG) was developed. By utilizing the wind-induced vibration of a fluorinated ethylene propylene (FEP) film between two copper electrodes, the S-TENG delivers an open-circuit voltage up to 36 V and a short-circuit current of 11.8 μA, which can simultaneously light up 20 LEDs and charge capacitors. Moreover, the S-TENG holds linearity between output current and flow rate, revealing its feasibility as a self-powered wind speed sensor. This work demonstrates potential applications of S-TENG in wind energy harvester, self-powered gas sensor, high altitude air navigation.

Cobalt/copper-codoped ZnO nanoparticles, synthesized with different Co concentrations by a sol–gel method using ethanol as solvent, were studied via XPS. Hexagonal wurtzite structure was found in all samples, with no evidence of any secondary phase. The average crystallite size of the samples was around 20–30 nm, altered significantly with increasing Co concentration. Copper ions and Cobalt ions are indeed substituted into the ZnO lattice at the Zn2+ site, as shown by XRD and XPS. Further studies showed dramatic changes of Cu valence from +2 to +1 as the Co concentration level exceeds 1%, accompanied by a blue-shift of the optical bandgap from 3.01 to 3.13 eV. Ferromagnetism of the Co-doped Zn0.95Cu0.05O thin films was observed and found to be tunable – a phenomenon associated with the valence state of the Cu ions and the existence of some defects like oxygen vacancies in the films.

A promising approach was proposed to enhance the responsivity of a ZnO nanowires array based photodetector with metal-semiconductor-metal structure through piezo-phototronic effect. The ZnO nanowires arrays were synthesized via hydrothermal method to function as both piezoelectric and light-trapping layer. The photoresponses of the ZnO nanowires based photodetector were tuned by the modulation of local Schottky barrier heights (SBH) at the metal-ZnO interfaces as a result of strain-induced polarization charges. Subjected to a −0.62% compressive strain, the responsivity of the prepared photodetector was increased by as much as 176%. Furthermore, the devices hydrothermally synthesized at 0.10 M have a larger photoresponse and higher stress sensitivity compared to the ones prepared at 0.05 M and 0.15 M. This work not only strengthens the fundamental understanding of piezo-phototronic effect on photodetectors but also provides an efficient means for optimization/improvement of piezoelectric semiconductor nanowires based optoelectronic devices.

For the fabrication of pyroelectric polyvinylidene fluoride (PVDF) film with high performance, a novel method is presented which combines the usual two steps of solution casting and stretching into one. It demonstrates that a stretch ratio as large as 15 as well as low quantity of defects and high uniformity are achieved by this new technique. The characterization results reveal that baking temperature (Tb) after stretching has significant and similar influences on relative β-phase fraction (Fβ), remnant polarization (Pr), dielectric constant and loss (e′ and e″) and pyroelectric coefficient of the samples; the highest pyroelectric coefficient, occurring at baking temperature of 80 °C without thermal poling, is 12.4 μC m−2 K−1, which is larger than that of the usually-stretched sample undergoing thermal poling. In addition, by using the prepared film as sensitive element, a novel chopperless pyroelectric infrared detector is constructed by electrostatically modulating the incident thermal irradiation; the measurement results demonstrate that the detector has excellent pyroelectric voltage response to the thermal radiation of the laser source and hot (warm) water with a sensitivity of 2.65 × 104 V/W, showing its good potential for fully flexible infrared detector and temperature sensor.

Approximately 22% of the 86 million people in the United States living with prediabetes are unaware of their condition. Detection of acetone in human respiration offers an effective and painless approach for the diagnosis of prediabetes. In this work, a wearable active acetone biosensor employing chitosan and reduced graphene oxide (RGO) as sensitive materials was developed to non-invasively diagnose prediabetes. When operated under 97.3% relative humidity at room temperature, the prepared chitosan and RGO composite film-based sensor exhibited a good sensing response of 27.89% under 10 ppm acetone in respiratory gases, which is about 5 times higher than the sensing response of pure chitosan film-based devices. In addition, finite element analysis and phase-field simulation were conducted to provide theoretical support for the active sensing mechanism. This work not only presents a wirelessly powered wearable active acetone biosensor, but also paves the way for a new method of non-invasive prediabetes diagnosis.

Cobalt-iron-codoped ZnO films were synthesized with different precursor sol pHs by a sol–gel method. All the samples possess hexagonal wurtzite structure, with no evidence of secondary phases. The average crystallite size of the samples was in the range of 10–40 nm, accompanying significant differences with the increase of the H + ion level. The Co/Fe ions are indeed substituted at the Zn 2+ site into the ZnO lattice, as shown by XRD and XPS. Strong ultraviolet emission, blue double emission and weak green emission peaks are observed in the photoluminescence spectra of all samples at room temperature. Further studies reveal that the bandgap energy of the ZnO films increases from 3.15 eV (pH = 5) to 3.24 eV (pH = 9). Enhanced room-temperature ferromagnetism is observed for the (Co, Fe)-codoped ZnO films at sol pHs lower than 8. Our work clearly establishes that the origin of room-temperature ferromagnetism in the (Co,Fe)-codoped ZnO films is linked to O vacancies, tunable by the sol pH.

Effects of Co doping concentration on the microstructure and the photoluminescent properties of Zn 0.95 Cu 0.05 O thin films synthesized by a sol–gel method were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, room-temperature photoluminescence, UV transmission spectrometer. An analysis of the O 1s peak of ZnO film showed that the concentration of oxygen vacancies increases with the Co doping level. We also revealed that the introduction of Co ions causes the valence state of Cu to change from +2 to +1 as the Co concentration level exceeds 1%. The E g of Zn 0.95 Cu 0.05 O films shows a blueshift from 3.01 to 3.14 eV with increasing Co doping level.

Wetting states of droplets on partially micro-grooved surfaces were investigated. Grooves were fabricated using soft lithography and the width of the grooves was smaller than the droplet diameter. On the partially micro-grooved surfaces, the apparent contact angle parallel to the grooves is larger than the one on the smooth surface, while the microstructures have little effect on the contact angle perpendicular to the grooves. Increasing the fraction of the grooved area and the surface energy of the surface will result in a more anisotropic droplet. When a droplet impinged upon these partially grooved surfaces, the spreading process was similar to that on a smooth surface. However, the recoiling process was found to be quite anisotropic. The grooves enhanced the recoiling velocity in the direction parallel to the grooves while hindering the recoiling process in the perpendicular direction. The recoiling process will become more anisotropic by increasing the fraction of the grooved area. The effect of the grooves on both the contact angle and the impinging process is independent of the groove width scale and is only dependent on the fraction of the grooved area in the Cassie state.

Hydrogen-bond acidic (HBA) polymers are well-established adsorbents for organophosphorus compounds and nitroaromatic explosives detection. In this paper, we report two HBA polymers for detection of styrene vapors based on 434-MHz surface acoustic wave (SAW) chemical sensors. These polymers, dubbed PLF and LSFA, are pendent hexafluoroisopropanol (HFIP)-group modified polysiloxanes, which were synthesized by one-step hydrosilylation reaction. Real-time response studies of these two sensors showed that they are highly sensitive to styrene vapors with excellent selectivity. After exposure to 5 mg/m3 styrene vapor, the frequency shifts of the PLF and LSFA sensors have increased by 6.3 kHz and 3.2 kHz, respectively. The polymers are 20-fold less sensitive to toluene than to styrene while they have comparable sensitivity to 1-butene. In situ infrared spectroscopy studies demonstrated that the polymer–styrene interaction is attributed to the OH/π hydrogen bond between HFIP groups of the polymers and the ethylene group of styrene molecules.

In this work, utility theory is introduced to optimum aerodynamic shape design under uncertainty (also called robust aerodynamic design). Specifically, utility theory is used to formulate the objective function of the optimization problem. The advantage of the proposed approach over the commonly used weighted sum method is that it does not require the use of weighting factors or the addition of constraints on the statistical moments. The polynomial chaos expansion metamodel with the least-angle regression and the hyperbolic truncation scheme are used to accelerate the uncertainty propagation and the optimization process. The proposed approach is demonstrated on the optimum airfoil shape design under uncertainty at steady transonic conditions. Two design cases are considered. In both cases the drag coefficient is to be minimized subject to constraints on the lift coefficient and the airfoil thickness at two chordwise locations. The first case treats the Mach number as uncertainty parameter and the second case treats the Mach number and the lift coefficient at target as uncertain. The proposed method is compared with deterministic single-point optimization and multi-point optimization, and the standard robust design formulations. Results show that the proposed approach is capable of obtaining airfoil design of the lowest mean drag coefficient with the smallest standard deviation as compared to the other approaches. In the first case, the proposed approach yields a design with a mean drag coefficient comparable to the standard robust design (around 97.6 drag counts, cts), but with a significantly lower variance (0.6 cts versus 2.5 cts). In the second case, the proposed approach yielded a design with a higher mean drag coefficient than the standard approach (98.4 cts versus 97.6 cts), but with a lower standard deviation (4.1 cts versus 4.8 cts). In both cases, the deterministic approaches yield designs with comparable or lower drag coefficients but with significantly larger standard deviations.

This work introduces multifidelity metamodeling for reliability analysis of nondestructive testing (NDT) systems. Specifically, the Cokriging metamodel is utilized to accelerate the uncertainty propagation within model-assisted probability of detection (MAPOD) analysis of ultrasonic testing (UT) systems. The Cokriging multifidelity metamodel fuses a limited amount of data obtained from high-fidelity (HF) physics-based UT models, which are accurate but time-consuming to evaluate, with a conservative to large amount of data from low-fidelity (LF) physics-based UT models, which are less accurate but faster to evaluate. The resulting Cokriging metamodel is fast to evaluate and yields an accurate estimate of the output of the HF model. The proposed approach is demonstrated on three benchmark UT MAPOD cases involving spherically-void and pill-box shaped defects in flat aluminum plates using planar and focused transducers. The results show that a two-level Cokriging metamodel is capable of yielding estimations of the HF model that are globally accurate within 1% of the standard deviation of the testing points. Furthermore, the result show that the Cokriging metamodeling approach needs around one order of magnitude fewer training data points when compared to the current state-of-the-art approaches that rely on metamodels constructed with Kriging.

Human respiration is rich in physiological and pathological information for health assessment and illness prediction. In this work, an integrated triboelectric self-powered respiration sensor (TSRS) was developed for simultaneously monitoring human respiratory behaviors and NH3 concentration in exhaled gases. The TSRS based on Ce-doping ratio of 0.004 M exhibits a better selectivity and larger sensitivity of 20.13 ppm−1 compared with those synthesized in other doping ratios. Under the same moisture as the breathing gas (97.5%RH), the sensor holds greater sensitivity toward NH3 at low concentration (0.1–1 ppm) than that at high concentration (1–10 ppm), implying the capability in detecting trace level NH3 biomarker in human breathing gases. Furthermore, triggered by the expansion and contraction of chest during breathing, TSRS can spontaneously monitor human respiratory patterns and physiological process after physical exercise. Meanwhile, a theoretical modeling was established in terms of permittivity change under gas molecules adsorption and verified via finite element simulation to interpret the self-powered sensing behaviors. This research not only proposes a promising approach to develop an all-in-one wearable respiration monitoring system for personal health diagnosis but also sheds some light on the theoretical modeling of triboelectric self-powered gas-sensing in terms of permittivity change.

Two kinds of toluene vapor sensors with different sensitive film structures, i.e., multi-walled carbon nanotubes (MWCNTs)-polyethylene oxide (PEO) composite film and MWCNTs-PEO bilayer film were fabricated. Both sensors were obtained by airbrushing the sensitive films on interdigitated electrodes (IDE). Response performances of both sensors to toluene vapor at room temperature were investigated. Scanning electron microscope (SEM) was used for morphology analysis of the sensitive films. The experimental results showed that sensors with bilayer films revealed a larger sensitivity than that with the composite films. The response and recovery times of both sensors were within 8 s. Moreover, sensors with bilayer films exhibited a modest selectivity to toluene vapor. The sensing mechanisms of both sensors were studied as well.

A new hexafluoroisopropanol groups functionalized hydrogen-bond acidic siloxane polymer for quartz crystal microbalance sensor (QCMs) application was synthesized via O-alkylation, Claisen rearrange, hydrosilylation and hexafluoroacetone groups (HFA) electrophilic addition reactions. This hexafluoroisopropanol-functionalized siloxane polymer was confirmed by FT-IR and 1H NMR, and coated onto an AT-cut 8 MHz QCM sensor to investigate its gas sensitive responses to eight different typical organic volatile chemical vapors. The results indicated that this new siloxane polymer exhibited an excellent performance on the detection of the organophosphorus nerve agent stimulant dimethyl methylphosphonate (DMMP) vapor, and the frequency changes of this functionalized siloxane polymer based QCM sensors to the DMMP vapor were completely linear and with a regression coefficient of 0.9993 in the concentration range of 10–60 ppm. In addition, the sensitivity of the fabricated QCM sensor to DMMP was up to 23.07 Hz/ppm, and it is much higher than that of the other chemical vapors under the same circumstances, the detection limits (LODs) of this fabricated QCM sensor was obtained as low as 0.13 ppm.

The polyaniline/PdO composite was synthesized by chemical oxidative polymerization of aniline with PdO nanoparticles. A methane gas sensor was made by deposition polyaniline/PdO thin films on a mass-type quartz crystal microbalance (QCM) device through layer-by-layer (LbL) self-assembly method. Scanning electron microscopy inspection shows that the polyaniline/PdO multilayers are formed with a dense network of nanofibers. The frequency responses of the polyaniline/PdO based QCM sensor to methane gas were measured at room temperature and 50 °C. It exhibited that the polyaniline/PdO based QCM gas sensor has a better response at room temperature than that at 50 °C. Meanwhile, the humidity effect is also discussed.

Quartz crystal microbalance (QCM) gas sensors based on polymeric material were fabricated and their gas response characteristics were examined for four simulant gases of chemical agents, which were dimethyl methyl phosphonate (DMMP), N,N-dimethylacetamide (DMA), 1,5-dichloropentane (DCP) and dichloroethane (DCE). For the selection of appropriate coating materials, both principal component analysis (PCA) and hierarchical cluster methods were applied to a data set collected from 15 QCM sensors for 12 analytes. Four appropriate coating materials were selected after optimizing the correlation between the 15 coating materials and the first four principal component (PC) factors. The four chosen polymers were used as sensitive component for a sensor array, and then PCA is adapted to classify four simulant gases. The results show that the QCM sensor array has high sensitivity and selectivity to four chemical agents.

A quartz crystal microbalance (QCM) modified with poly(vinylidene fluoride) (PVDF) was fabricated and used for detection of dimethyl methylphosphonate (DMMP) vapor, a simulant of nerve agents using a drop-coating method. Measurements were based on the frequency shifts due to the adsorption of DMMP vapor on the surface of the modified electrodes. It was found that frequency shifts were linear to the concentrations of analyte in the range of 5–60 ppm with a correlation coefficient of above 0.997. The influences of temperature and humidity on the sensors were also examined. Results showed that the sensitivity to DMMP vapor was almost identical in various humidity circumstances, and the sensitivity was higher in a lower temperature range.