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In this paper, three-point bending tests were carried out o investigate the post-peak cyclic loading behavior of dam concrete under two loading rates. The fracture parameters, residual load capacity, cyclic modulus, dissipated energy, and deformation recovery were presented and analyzed. The analysis was made to understand the evolution of fracture process zone (FPZ) under post-peak cyclic loading for dam concrete by utilizing digital image correlation (DIC) technique. The results showed while the dam concrete under a higher loading rate showed an increase in maximum load, it is not necessarily the same for post-peak bearing capacity. The specimens with higher post-peak bearing capacity had higher residual stiffness, higher dissipation energy, and higher Crack Mouth Opening Displacement (CMOD) reversibility under cyclic loading. The FPZ development was investigated quantitatively, and the extension and retraction of its tip were observed. Moreover, it was found that the FPZ in specimens with higher residual stiffness developed more slowly, and FPZ had a more significant retraction rate during unloading for the specimens with higher residual bearing capacity.

The development of pressure sensor arrays capable of distinguishing the shape and texture details of objects is of considerable interest in the emerging fields of smart robots, prostheses, human-machine interfaces, and artificial intelligence (AI). Here we report an integrated pressure sensor array, by combining solution-processed two-dimensional (2D) MoS2 van der Waals (vdW) thin film transistor (TFT) active matrix and conductive micropyramidal pressure-sensitive rubber (PSR) electrodes made of polydimethylsiloxane/carbon nanotube composites, to achieve spatially revolved pressure mapping with excellent contrast and low power consumption. We demonstrate a 10 × 10 active matrix by using the 2D MoS2 vdW-TFTs with high on-off ratio > 106, minimal hysteresis, and excellent device-to-device uniformity. The combination of the vdW-TFT active matrix with the highly uniform micropyramidal PSR electrodes creates an integrated pressure sensing array for spatially resolved pressure mapping. This study demonstrates that the solution-processed 2D vdW-TFTs offer a solution for active-matrix control of pressure sensor arrays, and could be extended for other active-matrix arrays of electronic or optoelectronic devices.

In the present paper, a digital image correlation (DIC) method is used to study the development of fracture process zones (FPZ) of different concrete materials in three-point bending test. Different concrete materials including original concrete, rubber concrete, self-compacting rubber concrete and pervious concrete are investigated. Firstly, the image of the FPZ and the crack opening displacement (COD) in FPZ is obtained by acquiring strain field and displacement field information. The relationship between the development of FPZ and the mechanical properties is further studied. It is found that there is a strong correlation between the FPZ and the post-peak strength reduction of concrete. The development characteristics of FPZ of different concrete materials are analyzed. The addition of rubber will result in stronger strain concentration in pre-peak stage compared to original concrete, and the FPZ will emerges at the earlier loading stage, but it can enhance the crack resistance of concrete in the post-peak stage. Self-compacting rubber concrete was observed to have higher bearing capacity and cracking resistance during fracture than that of the others. Pervious concrete has weak resistance to fracture, and there is almost no decline of the FPZ development rate in fracture process.

Low density polyethylene (LDPE) film samples with the surface treatment by silver nanoparticles based on the biomimetic dopamine technology are obtained and the influence of the treatment on the space charge behavior as well as DC breakdown performance of the selected insulating system is studied. The results obtained by the energy dispersive spectrometer and the scanning electron microscope indicate that Ag particles with nanoscale or larger size form and distribute uniformly on the surface of LDPE modified in the dopamine solution, silver nitrate solution (AgNO3) and dopamine solution in sequence. Space charge profile measured by the pulsed electro-acoustic method shows that homo-charge injection is suppressed with proper surface treatment. DC breakdown strength increases initially and then decreases with the increase of the size of Ag particles. The electrical breakdown strength of the specimen D6-Ag1-D24 is the highest, which increases by 9.5% compared with that of untreated LDPE. Finally, it is considered that the treatment of LDPE based on the biomimetic dopamine technology changes the chemical and physical properties of the surface through forming a three-layer structure, which plays a similar role as the nano-dielectrics. Such treatment can impact the space charge injection and accumulation, and further the corresponding DC breakdown strength, which provides a novel method to optimize the dielectric strength of the polymeric insulating materials.

In this paper, surface trap distribution and the affected surface charge transport properties in epoxy/Al2O3 nanocomposites were studied to provide theoretical and experimental basis for improving surface flashover performance in vacuum. Four different contents of nano-Al2O3 particles were doped into epoxy and different trap distribution of samples was calculated from the surface potential decay method. Surface charge injection was identified by a direct current integrated charge [DCIC-Q(t)] method. Secondary electron emission (SEE) coefficient were obtained combing testing and fitting method. Results showed improved charge injection resistance, reduced charge mobility and SEE coefficient at a slight concentration of 0.5 wt% and 1 wt% by introducing deep traps. Continuing to increase nanoparticles in matrix was proved to reduce trap depth and have adverse effects. The surface flashover voltages reached the highest at 1 wt% nano-doping, which was in accordance with the percolate threshold loading content for trap depth, charge injection field and SEE coefficient. Surface charge injection caused the local field enhancement at the counter electrode and increased the possibility of surface flashover. Deep traps over 1 eV contributed to carrier capture, reduced charge injection and had a positive effect on increasing surface flashover voltage.

Ethylene propylene diene monomer (EPDM) is a polymer widely used for insulation in high voltage outdoor insulators and cables. It is well accepted that appropriate addition of micron particles to form a composite can enhance its insulation performance. This work reports improvement on the dielectric breakdown strength, tracking failure time, mechanical properties and volume resistivity of EPDM composites co-filled with boron nitride (BN) micron and nano–particles. Test specimens were fabricated by melt-blending and hot press techniques. AC breakdown tests were performed as per IEC60243-1 Standard. The tracking test was performed following IEC 60587 Standard and volume resistivity measurement as per ASTM D257. Experimental results show improvement in electrical properties with increasing particle loading up to a certain dosage but enhancement in the mechanical properties is observed up to 30 wt% particles addition. The co-filled composite exhibits considerably higher dielectric breakdown strength (89.24 kV/mm) and volume resistivity (~ 5.0 × 1015 Ω cm) relative to Micro-20 wt%. The tracking failure time of the co-filled is much improved due to excellent resistance against dry band arcing and thermal accumulation in the discharge region. Moreover, co-filled composites show improvement in mechanical properties as compared to the micron–filled counterparts. The improved thermal conductivity, better thermal stability and overall higher surface area of the particles are possible factors which impart better performance to the co-filled composites.

In the limited space on the roof of the high-speed train, breakdown performance of the high voltage box can be greatly improved by introducing the insulation barrier between bus-bar and ground plane. In the paper, effect of barrier size, position and material property on ac air gaps breakdown voltage have been studied, and two typical barrier materials, polyester glass blanket (GPO-3) and epoxy resin (EP) have been compared. Further, surface potential property on the barrier after discharge has been measured by the non-contact surface potentiometer, and surface trap parameters of the two materials have been calculated. The experimental results indicate that the breakdown voltage of rod-plane gaps will be increased about 1.95 times and 1.83 times for GPO-3 and EP respectively. On the one hand, the discharge path can be lengthened by increasing the size of the barrier. On the other hand, the closer the barrier to the rod electrode, the evolution of corona region can be prevented as soon as possible before the self-holding discharge occurs. There exists obvious residual charges on the barrier surface after discharge, the initial surface potential of EP and GPO-3 after discharge are 8091 V and 3856 V respectively. Further, it has been calculated that the trap levels of the two barriers are both the deep trap, about 1.0 eV, resulting in that the residual charges remain on the barrier surface for a long time. In addition, the residual charge density of EP is more than that of GPO-3, the charge density peaks of EP are 3.33 × 1019/m3 and 2.75 × 1019/m3, which is the main reason that its breakdown voltage is lower than that of GPO-3.

An amendment to this paper has been published and can be accessed via the original article.

Breakdown performance of polymer under high voltage direct current (DC) and alternating current (AC) fields is receiving more and more attentions with the ever-increasing demand of raising voltage class and developing long-distance transmission. The existing researches indicate that space charge should play an important role in influencing breakdown performance. However, two key issues, that the different effects of space charge on DC breakdown strength (FDC) and AC breakdown strength (FAC), and that the reason for FDC being always higher than FAC, remain not completely clear. In this letter, we study the mechanism of DC and AC breakdown by modulating space charge distribution in low density polyethylene by using direct fluorination process. The results show that FDC closely relates to the space charge modulation under DC field but FAC almost has nothing to do with it. Therefore, direct fluorination process can be used to modulate space charge distribution under DC field and further FDC. DC breakdown models with both homocharge and heterocharge distributions are proposed. They ascribe DC breakdown to field distortion induced by space charge and large defects caused by energetic processes, which happen in middle bulk under homocharge distribution and in marginal bulk under heterocharge distribution. FAC being still lower than FDC with heterocharge distribution proves the important influence of the energetic processes happening at polymer/electrode interface and in marginal bulk, besides the field enhancement caused by heterocharge. The modulation mechanism is discussed combined with trap characteristics of carriers.

As compared with polymer semiconductors, solution-processed small-molecule semiconductors usually have poorer film-formation properties, which induces wide variations in device performance in terms of mobility and threshold voltage, thus severely limiting their commercial applications. In this work, we propose an easily accessible method to improve the performance and reduce the variability of small-molecule organic field-effect transistors (OFETs) by blending organic semiconductors with an insulator polymer, which is subsequently post-treated by gate stress to generate an electret. By blending the organic semiconductor 2,7-didodecyl[1]benzothieno[3,2-b][1]benzothiophene (C12-BTBT) with the insulator polystyrene, uniform transport layers with vertically phase segregated morphology are obtained, from which the mobility and threshold voltage of OFETs are largely manipulated. The OFETs exhibit field-effect mobilities as high as 7.5 cm2·V−1·s−1 with an on/off ratio exceeding 106 in ambient conditions. This double-layer structure provides an appropriate architecture for applying gate-stress to inject charges into the insulating layer, forming an electret. The generation of the electret is thermally accelerated and thus can be easily realized under moderate gate-stress at elevated temperature (e.g., 60 °C). After cooling, the electret layer serves as a floating-gate, which not only continuously tunes the threshold voltage and field-effect mobility, but also helps minimize the contact resistances and optimize the subthreshold swing. As an application of this method, a digital inverter is built and its performance is optimized via in situ tuning of its individual transistors.

X-ray photoelectron spectroscopy has been used to measure the band alignment the In2Se3 multilayers (MLs)/ZnO heterojunction. The MLs In2Se3 was fabricated by pulse laser deposition (PLD) on ZnO/Al2O3 substrates. The valence-band offset (ΔEv) of In2Se3 MLs/ZnO is determined to be 2.19 ± 0.1 eV, and the conduction-band offset (ΔEc) is deduced to be 0.96 ± 0.1 eV, indicating that In2Se3-MLs/ZnO heterojunction has a type-II band alignment.

Effects of dc bias on dielectric relaxations in CaCu3Ti4O12 ceramics were investigated via an improved dielectric spectroscopy. A new low-frequency dielectric relaxation, which was assigned to space charge polarization, was found shifting towards higher frequency with increasing bias voltage in the improved spectra. It was suggested that the Schottky barrier at grain boundary was lowered under dc bias resulting in higher possibility for carriers to migrate. Therefore, the relaxation time was decreased, which was in accordance with rightward shift of this relaxation under increased dc bias. In addition, dependence of the widely reported high-frequency relaxation (> 105 Hz) and middle-frequency relaxation (103–105 Hz) on bias voltage was also discussed. Permittivity contributed by either high-frequency or middle-frequency relaxation presented inverse dependence on dc bias. Discrepancy on barrier parameters was obtained assuming both of them physically correlated with the barrier at grain boundary.

The role of alkali metal elements in ZnO varistor is of interest because of the small ion radius and valence state. They are expected to form acceptor state and convert the n-type ZnO grain to p-type. However, researches to manufacture p-type ZnO semi-donductor by using alkali metal elements have failed. In the present work, the effects of lithium element on the defect structures, microstructures and corresponding electrical performances of ZnO varistors is investigated. According to the obtained results, the influences of lithium element on the defect structures of ZnO varistors will vary with the amount of lithium. Lithium ion occupies the interstitial site of ZnO grain at first and then occupies the substitutional site. Trace amount of lithium (0.0005–0.002 wt%) can reduce the residual voltage of ZnO varistors while the E–J characteristics at low current region remain stable.

99 Tc m -octreotide scintigraphy and serum eye muscle antibodies in evaluation of active thyroid-associated ophthalmopathy

In this review paper detailed development of the ZnO–Bi2O3 based polycrystalline varistors are presented as the technological importance emerged with the rapid applications of the gapless surge protectors superseding traditional gapped SiC designs. The excellent symmetric nonlinear current–voltage (I–V) characteristic of these varistors results from the type of back-to-back electrical potential barriers that are formed between the successive ZnO grains during the step-wise processing cycles. The role of microstructures and the defect structures in conjunction with the processing parameters paved the road to the understanding of the degradation and failure mechanisms of the electrical potential barriers for acceptable protective characteristics. The nature of the processing variables influencing eventual performance of varistors is discussed.

The influences of CuAl2O4 doping on the microstructure, dielectric properties and relaxations of CaCu3Ti4O12 ceramics have been studied in the paper. The dielectric properties were measured under the frequency from 10−1 to 107 Hz and the temperature from 153 to 453 K. An enhanced breakdown electric field, associated with lower dielectric loss at low frequency has been obtained via adding CuAl2O4. Three Dielectric relaxation processes are found in the frequency dependence of modulus planes. The activation energy of 0.10 eV, barely varies with CuAl2O4 addition, and is attributed to the intrinsic electronic relaxation. The energy level decreasing from 0.50 to 0.22 eV with the addition of CuAl2O4 may be caused by multi impurities and boundaries. The energy of conduction process varies from 0.66 to 0.86 eV, which showed elevated energy barrier for hopping of charge carriers and can be attributed to the blocking effect of more grain boundaries. The barriers at grain boundary of the samples collapsed with excessive content of CuAl2O4, which led to the absence of non-ohmic properties and high dielectric constant.

Ultrafine BaTiO3, unlike traditional ferroelectric materials, demonstrates some interesting dielectric properties, such as a gradual transition from paraelectric to ferroelectric phase, which is similar to dielectric relaxation ferroelectrics. Although several methods have been recently proposed to measure the dielectric properties of ultrafine BaTiO3, the problem still remains unsolved. This paper proposes a new method to estimate the dielectric properties of ultrafine BaTiO3 by measuring and analyzing the dielectric properties of BaTiO3-epoxy composites. The Novocontrol dielectric measuring system was employed to measure the dielectric response of the composites. The dielectric behavior and relaxation characteristics of the BaTiO3 filler were estimated by modeling and calculating the dielectric constant based on different mixture theories. Results reveal that the effect of surface states yields dielectric relaxation in ultrafine BaTiO3.

The effect of sintering temperature (ranging from 1055 to 1200 °C) on the phase ingredient and dielectric property of the nominal BaTi2O5 ceramics (starting with the Ba/Ti of 1:2) fabricated by a spark plasma sintering method were systematically studied. At the first stage, BaTi2O5 component was enhanced in the sintering temperature range of 1055–1120 °C; it turned out to be the dominant phase. For these BaTi2O5 phase dominated ceramics, the Curie temperature T c rised on increasing the sintering temperature and saturated around 440 °C with the maximum dielectric constant of 500. Further increasing the sintering temperature, the decomposition of the obtained BaTi2O5 into BaTiO3 extensively happened; the ceramics turned to be the BaTi2O5 and BaTiO3 coexisting state. These ceramics can be characterized by two dielectric anomalies. One at ~420 °C stood for the phase transition of BaTi2O5 while the other at ~150 °C stood for the transition of BaTiO3, which is exceptionally high as the normal BaTiO3 ceramics. Further increasing the sintering temperature (until 1200 °C) would dramatically enhance the BaTiO3 phase; the ceramics showed T c at 130 °C with the maximum dielectric constant of 1800.

Optimal switch-time control is the study that investigates how best to switch between different modes. In this paper, we investigate the optimal switch-time control problem for discrete-time linear switched stochastic systems. In particular, under the assumption that the sequence of active subsystems is pre-specified, we focus on the problem where the objective is to minimize a cost functional defined on the states and the switching times are the only control variables. For systems with one switching time, using calculus of variations, we firstly derive the difference formulae of the cost functional with respect to the switching time, which can be directly used to find the optimal switching instant. Then, a method is presented to deal with the problem with multiple switching times case. Finally, the viability of the proposed method is illustrated through two numerical examples.

The dielectric properties of CaCu3Ti4O12 ceramics fabricated with nano-size fine powders (~30 nm) are compared with that fabricated with micro-size coarse powders (0.1–0.3 μm). For the same sintering conditions, the ceramic samples with nano-size fine powders have more uniform and denser microstructures and higher room temperature dielectric constant (~105, in the frequency range of 10−1–105 Hz) than that with micro-size coarse powders. That the use of nano powders facilitates the formation of Cu-rich amorphous phase in the grain boundary led to an increasing dielectric loss in low frequency range. Besides the common intrinsic defect structure of V O + and V O ++ , the energy level of ~0.72 eV detected in high temperature range is attributed to the conduction relaxations, and the energy level of 0.30–0.40 eV which is only detected in the sample synthesized by common submicron powders is suggested to originate from the defect level of grain boundary related to Cu ions. This research provides a technical guidance for the application of this material.

Electrical breakdown is one of the most important physical phenomena in electrical and electronic engineering. Since the early 20th century, many theories and models of electrical breakdown have been proposed, but the origin of one key issue, that the explanation for dc breakdown strength being twice or higher than ac breakdown strength in insulating materials, remains unclear. Here, by employing a bipolar charge transport model, we investigate the space charge dynamics in both dc and ac breakdown processes. We demonstrate the differences in charge accumulations under both dc and ac stresses and estimate the breakdown strength, which is modulated by the electric field distortion induced by space charge. It is concluded that dc breakdown initializes in the bulk whereas ac breakdown initializes in the vicinity of the sample-electrode interface. Compared with dc breakdown, the lower breakdown strength under ac stress and the decreasing breakdown strength with an increase in applied frequency, are both attributed to the electric field distortion induced by space charges located in the vicinity of the electrodes.

Sparse Representation Method has been proved to outperform conventional face recognition (FR) methods and is widely applied in recent years. A novel Kernel-based Sparse Representation Method (KBSRM) is proposed in this paper. In order to cope with the possible complex variation of the face images caused by varying facial expression and pose, the KBSRM first uses a kernel-induced distance to determine N nearest neighbors of the testing sample from all the training samples. Then, in the second step, the KBSRM represents the testing sample as a linear combination of the determinate N nearest neighbors and performs the classification by the representation result. It can be inferred that the N nearest training samples selected are closer to the test sample than the rest, so using the N nearest neighbors to represent the testing sample can make the ultimate classification more accurate. A number of FR experiments show that the KBSRM can achieve a better classification result than the algorithm mentioned in Xu et al. (Neural Comput Appl doi: 10.1007/s00521-012-0833-5 ).

The problem of delay-dependent stability analysis and controller design for a class of T-S fuzzy systems with interval state time-varying delay is considered. Based on Lyapunov stability theory, defining a new Lyapunov-Krasovskii functional and introducing some free-weighting matrices, a new delay-dependent criterion is given to ensure the systems asymptotically stable. The merit of the proposed conditions lies in the less conservativeness than the existing ones, which is achieved by considering the mean of time-delay interval and the introduction of the free variables. By the concept of parallel distributed compensation (PDC), a delay-dependent condition for the existence of a fuzzy state feedback control law with memory is proposed. Another merit is the consideration of the memory of the controller. All conditions are shown in terms of linear matrix inequalities (LMIs), which can be solved efficiently by using the LMI optimization techniques. Two numerical examples are given to illustrate the feasibility and validity of the proposed approach.

Polyimide (PI)-matrix composite films containing inorganic nanoparticles (nano-Al2O3 and nano-TiO2) have been fabricated. A proposed model is used to explain different structures of the (Al2O3–TiO2)/PI (ATP) films synthesized by employing in situ polymerization. Dependences of dielectric permittivities of the ATP films on frequency and temperature were studied. Results show the breakdown strength of the films decreases with prolonging the corona aging time. The incorporation of the nano-Al2O3 and nano-TiO2 particles significantly improves the corona resistance of the films. The corona aging also influences the infrared absorbance, the glass transition temperature (Tg), and loss factor (tanδ) of the ATP films.

The improvement of the voltage gradient and energy-handling capability of the ZnO varistors is necessary for reliability and protection level in conjunction with the reduced mass of the surge arresters. The varistor processing variables were investigated and then energy-handling capabilities were evaluated. To reduce influence on the chemical co-precipitation process the method of fractional precipitation on seeds was used. In this study the influence of precipitant, dispersant, pH value, and temperature on the uniformity of the sediments and calcined additive powders was evaluated. It was observed that when the sediments were dried by the “half-dry” method via calcination in the range 600–650 °C, the calcined powders of the additives obtained had either no agglomeration or little agglomeration of the particles. The influence of the additive powders on spray dried granules and their forming were also studied. Eventually ZnO varistor blocks possessing varistor voltage gradient in the range 210∼260 V/mm and the energy handling capability of about 270 J/cm3 have been achieved.

The microstructural effect on the electrical properties of SrTiO3 based varistor-capacitor materials sintered at various atmospheric conditions is investigated. Three sintering atmospheres are used by the decomposing source of liquid ammonia: (a) 30% H2 + 70% N2, (b) 50% H2 + 50% N2, and (c) 75% H2 + 25% N2 besides sintering in regular air as ambient. It is found that with the percentile increase of H2 in the sintering atmosphere, the grain size and carrier concentration increase while varistor voltage V 10mA and nonlinear coefficient α decrease. It is suggested that more oxygen vacancies can be produced in strong reducing atmospheres, and the grain growth process is then controlled by the grain boundary diffusion, which leads to a lower sintering temperature. The results of Positron Annihilation Technique reveal that higher free carrier concentration can be generated that aids in changing electrical properties.

The post-sintering heat treatment on the current-voltage behavior of the ZnO-Bi2O3 based varistors is reported. It is suggested that only phase transition of the Bi2O3 is not alone responsible for the resulting electrical performance by these devices. The ambient condition influences the performance parameters. Thus, incorporating the role of oxygen and zinc interstitial in the total device during the post-sintering heat-treatment is accounted as responsible parameters for the ultimate performance. Two recipes are used in demonstrating the effect of heat-treatment on the functional behavior of the devices.

The role of oxygen in the heat-treatment process of SrTiO3 varistor ceramics has been investigated in this paper. The varistor voltage of SrTiO3 ceramics has been found to be independent of the sample thickness and it increases with the heat-treatment temperature. It has been further revealed that the dielectric property is mainly governed by a highly resistive surface layer. The XPS results of Mn 2p and O 1s suggest that the surface layer is formed by oxygen diffusion and surface chemisorption at grain boundaries during the heat treatment in air. The chemisorption of oxygen in grain boundaries, which leads to the highly resistive surface layer, is the origin of the varistor property of SrTiO3 ceramics.

There are a number of gas ionization sensors using carbon nanotubes as cathode or anode. Unfortunately, their applications are greatly limited by their multi-valued sensitivity, one output value corresponding to several measured concentration values. Here we describe a triple-electrode structure featuring two electric fields with opposite directions, which enable us to overcome the multi-valued sensitivity problem at 1 atm in a wide range of gas concentrations. We used a carbon nanotube array as the first electrode, and the two electric fields between the upper and the lower interelectrode gaps were designed to extract positive ions generated in the upper gap, hence significantly reduced positive ion bombardment on the nanotube electrode, which allowed us to maintain a high electric field near the nanotube tips, leading to a single-valued sensitivity and a long nanotube life. We have demonstrated detection of various gases and simultaneously monitoring temperature, and a potential for applications.