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Semantic segmentation is used in many fields, and most fields not only require models with high-quality predictions but also require real-time speed in the forward inference phase. Therefore, our goal is to perform high-quality real-time semantic segmentation, thus proposing the feature pyramid aggregation network (FPANet). This network can be regarded as an encoder-decoder model. In the encoder stage, we use ResNet and atrous spatial pyramid pooling (ASPP) to extract more high-level semantic information. In the decoder stage, to simultaneously obtain the semantic and spatial information of the image, we propose a bilateral directional feature pyramid network for semantic segmentation to fuse features at different levels, it is named SeBiFPN. In SeBiFPN, we design a lightweight feature pyramid fusion module (FPFM) to fuse features from two different levels. In addition, when predicting the border region of an image, most real-time semantic segmentation models perform poorly; therefore, we propose a border refinement module (BRM) to improve the problem of inaccurate border segmentation. To reduce the computational complexity of the model, we redesign the ASPP module and reduce the number of feature channels during feature fusion. Our method achieves a better balance of speed and accuracy compared to the state-of-the-art methods on the Cityscapes and CamVid datasets.

Polymer dielectrics with available energy storage performance at high temperatures are critical to meet the demands of emerging applications such as hybrid electric vehicles (HEVs), wind turbine generators, and oil and gas exploration. But the dielectric properties of most engineering polymers with thermotolerance rapidly deteriorate with temperature rising. Here, polyetherimide (PEI) nanocomposite films containing Al2O3 nanoparticles (AO-nps) were fabricated by a solution casting method. The dielectric properties, breakdown strength, and energy storage performances of PEI/AO-nps nanocomposites were investigated from 25 °C to 150 °C. With the introduction of AO-nps, the breakdown strength of the nanocomposites was greatly improved at high temperatures because AO-nps significantly inhibit the injected charges. The 1 vol% PEI/AO-nps nanocomposite exhibits excellent capacitive performance, e.g., a discharge energy density of 3.70 J cm−3 with a charge–discharge efficiency of 90.1% evaluated at 500 MV m−1 and 150 °C, which is the maximal value compared with the state-of-the-art counterparts. The high-temperature applicability of the present nanocomposite film makes it promising in manufacturing dielectric energy storage devices for harsh environments.

TiO2 nanofibers embedded with BaTiO3 nanoparticles (BTO@TO_nfs) are prepared by electrospinning method. The interfacial effects of nanofibers on the dielectric relaxation processes of poly (vinylidene fluoride-trifluroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) are studied in a temperature range of −30 °C–96 °C. Two relaxation processes are investigated, i.e. space charge relaxation and α relaxation, which could be described by Arrhenius equation and Vogel-Fulcher-Tamman (VFT) equation, respectively. The results show that the addition of BTO@TO_nfs decreases the activation energy for space charge relaxation due to the shortened distance for charge motion, while the energy needed for α relaxation also decreases as a result of the suppressed intermolecular cooperativity by the BTO@TO_nfs. Homogeneous dispersion of the nanofibers in matrix also promotes the local homogeneity of polymer chains, resulting in a narrower distribution of relaxation times for α relaxation.

Emerging dielectric composites consisting of polymer and ceramic nano-inclusions or several polymers facilitate the development of capacitive energy storage materials, as they can preserve high breakdown strength and exhibit enhanced dielectric constant. Ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymers have been intensively studied as the matrices because of their high intrinsic dielectric constant and breakdown strength. Here, we review the recent advances on improving the energy density of PVDF-based composite dielectrics. It is concluded that, promotion of energy density is mainly established on enhanced breakdown strength and improved discharge efficiency. The microstructure design, material performance, and mechanism associated with these parameters are described. Perspectives for future development on PVDF-based nanocomposites and application of other potential polymer matrices are presented at last.

Through the modulation of the dipolar entropy under an applied electric field (E), a reversible temperature change (ΔT) could be achieved in a dielectric material, which is known as the electrocaloric (EC) effect. Among all EC materials, ferroelectric terpolymer P(VDF-TrFE-CFE) has been regarded as one of the most promising EC materials owing to its large EC effect and superior thermal stability. Yet, the low EC strength limits the application of terpolymers in realistic cooling devices. In this work, using the thermal treatment of quenching and low-temperature annealing, the terpolymers with significantly decreased crystalline size are prepared with their EC performances investigated. Compared to the normal ones, the terpolymers with smaller crystalline size exhibit substantially enhanced EC strength. The better EC performance may be mainly attributed to the lower energy barriers for dipole orientation, which gives rise to higher polarization at low electric fields. This work emphasizes the critical role of crystalline size on the macroscopic properties of EC polymers. Keywords: Electrocaloric effect, P(VDF-TrFE-CFE), Crystalline size

Purpose We have developed a second-generation virtual-pinhole (VP) positron emission tomography (PET) device that can position a flat-panel PET detector around a patient's body using a robotic arm to enhance the contrast recovery coefficient (CRC) and detectability of lesions in any region-of-interest using a whole-body PET/computed tomography (CT) scanner. Methods We constructed a flat-panel VP-PET device using 32 high-resolution detectors, each containing a 4 × 4 MPPC array and 16 × 16 LYSO crystals of 1.0 × 1.0 × 3.0 mm3 each. The flat-panel detectors can be positioned around a patient's body anywhere in the imaging field-of-view (FOV) of a Siemens Biograph 40 PET/CT scanner by a robotic arm. New hardware, firmware and software have been developed to support the additional detector signals without compromising a scanner's native functions. We stepped a 22 Na point source across the axial FOV of the scanner to measure the sensitivity profile of the VP-PET device. We also recorded the coincidence events measured by the scanner detectors and by the VP-PET detectors when imaging phantoms of different sizes. To assess the improvement in the CRC of small lesions, we imaged an elliptical torso phantom measuring 316 × 228 × 162 mm3 that contains spherical tumors with diameters ranging from 3.3 to 11.4 mm with and without the VP-PET device. Images were reconstructed using a list mode Maximum-Likelihood Estimation-Maximization algorithm implemented on multiple graphics processing units (GPUs) to support the unconventional geometries enabled by a VP-PET system. The mean and standard deviation of the CRC were calculated for tumors of different sizes. Monte Carlo simulation was also conducted to image clusters of lesions in a torso phantom using a PET/CT scanner alone or the same scanner equipped with VP-PET devices. Receiver operating characteristic (ROC) curves were analyzed for three system configurations to evaluate the improvement in lesion detectability by the VP-PET device over the native PET/CT scanner. Results The repeatability in positioning the flat-panel detectors using a robotic arm is better than 0.15 mm in all three directions. Experimental results show that the average CRC of 3.3, 4.3, and 6.0 mm diameter tumors was 0.82%, 2.90%, and 5.25%, respectively, when measured by the native scanner. The corresponding CRC was 2.73%, 6.21% and 10.13% when imaged by the VP-PET insert device with the flat-panel detector under the torso phantom. These values may be further improved to 4.31%, 9.65% and 18.01% by a future dual-panel VP-PET insert device if DOI detectors are employed to triple its detector efficiency. Monte Carlo simulation results show that the tumor detectability can be improved by a VP-PET device that has a single flat-panel detector. The improvement is greater if the VP-PET device employs a dual-panel design. Conclusions We have developed a prototype flat-panel VP-PET device and integrated it with a clinical PET/CT scanner. It significantly enhances the contrast of lesions, especially for those that are borderline detectable by the native scanner, within regions-of-interest specified by users. Simulation demonstrated the enhancement in lesion detectability with the VP-PET device. This technology may become a cost-effective solution for organ-specific imaging tasks.

High-energy-density dielectric materials are highly desirable for the miniaturization and integration of modern electronics and power modules for applications in electrical power, communication, medical and defense systems. However, the conventional polymer nanocomposites with nanofillers randomly dispersed exhibit a limited energy storage performance (e.g. discharged energy density

Poly(vinylidene fluoride) (PVDF)-based dielectric polymers are in great demand for the future electronic and electrical industry because of their high dielectric constants and energy density. However, some issues that limit their practical applications remain unsolved. One of the most urgent issues is their high dielectric loss and hence low efficiency. In this contribution, we proposed and demonstrate that substantially enhanced discharge efficiency of PVDF-based polymers nanocomposites could be achieved by simultaneously optimizing their topological-structure and phase composition. In the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP))/poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorofluoroethylene) (P(VDF-TrFE-CFE)) multilayered nanocomposites fabricated by non-equilibrium process, an ultrahigh discharge efficiency of ~85% is achieved up to 600 MV/m, which is the highest discharge efficiency reported so far for any polar-polymer dielectric materials at such high electric field. By adjusting the quenching temperature, the phase-composition hence dielectric permittivity in the terpolymer layers could be tuned for suppressed ferroelectric loss. Results of phase-field simulations further reveal that local electric field is substantially weakened at the interfaces between the Co/Ter polymer layers, which will act as barriers to motion of charge carriers and give rise to much suppressed conduction loss and a remarkably enhanced breakdown strength. Synergy of the optimized topological-structure and phase-composition thus leads to a nanocomposite that exhibits an unprecedented high discharge efficiency of the multilayered nanocomposites that is comparable to the bench-mark biaxially oriented polypropylene (BOPP) at high electric field as well as a high discharge energy density that is over 10 times higher than that of BOPP.

Purpose We investigated the feasibility of a novel positron emission tomography (PET) system that provides near real-time feedback to an operator who can interactively scan a patient to optimize image quality. The system should be compact and mobile to support point-of-care (POC) molecular imaging applications. In this study, we present the key technologies required and discuss the potential benefits of such new capability. Methods The core of this novel PET technology includes trackable PET detectors and a fully three-dimensional, fast image reconstruction engine implemented on multiple graphics processing units (GPUs) to support dynamically changing geometry by calculating the system matrix on-the-fly using a tube-of-response approach. With near real-time image reconstruction capability, a POC-PET system may comprise a maneuverable front PET detector and a second detector panel which can be stationary or moved synchronously with the front detector such that both panels face the region-of-interest (ROI) with the detector trajectory contoured around a patient's body. We built a proof-of-concept prototype using two planar detectors each consisting of a photomultiplier tube (PMT) optically coupled to an array of 48 × 48 lutetium-yttrium oxyorthosilicate (LYSO) crystals (1.0 × 1.0 × 10.0 mm3 each). Only 38 × 38 crystals in each arrays can be clearly re-solved and used for coincidence detection. One detector was mounted to a robotic arm which can position it at arbitrary locations, and the other detector was mounted on a rotational stage. A cylindrical phantom (102 mm in diameter, 150 mm long) with nine spherical lesions (8:1 tumor-to-background activity concentration ratio) was imaged from 27 sampling angles. List-mode events were reconstructed to form images without or with time-of-flight (TOF) information. We conducted two Monte Carlo simulations using two POC-PET systems. The first one uses the same phantom and detector setup as our experiment, with the detector coincidence re-solving time (CRT) ranging from 100 to 700 ps full-width-at-half-maximum (FWHM). The second study simulates a body-size phantom (316 × 228 × 160 mm3 ) imaged by a larger POC-PET system that has 4 × 6 modules (32 × 32 LYSO crystals/module, four in axial and six in transaxial directions) in the front panel and 3 × 8 modules (16 × 16 LYSO crystals/module, three in axial and eight in transaxial directions) in the back panel. We also evaluated an interactive scanning strategy by progressively increasing the number of data sets used for image reconstruction. The updated images were analyzed based on the number of data sets and the detector CRT. Results The proof-of-concept prototype re-solves most of the spherical lesions despite a limited number of coincidence events and incomplete sampling. TOF information reduces artifacts in the reconstructed images. Systems with better timing resolution exhibit improved image quality and reduced artifacts. We observed a reconstruction speed of 0.96 × 106 events/s/iteration for 600 × 600 × 224 voxel rectilinear space using four GPUs. A POC-PET system with significantly higher sensitivity can interactively image a body-size object from four angles in less than 7 min. Conclusions We have developed GPU-based fast image reconstruction capability to support a PET system with arbitrary and dynamically changing geometry. Using TOF PET detectors, we demonstrated the feasibility of a PET system that can provide timely visual feedback to an operator who can scan a patient interactively to support POC imaging applications.

Polymer nanocomposites are considered as promising dielectric media for electrostatic capacitors which are critical energy storage devices for pulse power applications due to their ultrahigh power density, superior cycle lifetime and reliability. The maximum energy density of percolative nanocomposites filled with conductive fillers is seriously compromised by their intrinsically low breakdown strength despite their very high dielectric permittivity. Here we demonstrate that a trace amount of Ag nanodots (∼0.05 vol%) in situ synthesized in a poly(vinylidene fluoride-hexafluoropropylene) matrix gives rise to concomitant enhancement of dielectric permittivity (∼50%) and breakdown strength (∼15%) and hence ultrahigh discharge energy density (∼27 J cm−3), which is the highest energy density ever achieved for percolative polymer composites. Experimental and first principles calculation results show that the non-intuitive enhancement could be attributed to charge-transfer complexes formed between the nanodots and the polymer chains and enhanced chain mobility in an electric field.

For the past decade, a novel cooling technique based on electrocaloric (EC) materials has been intensively investigated as an environmentally friendly and highly efficient alternative to the conventional vapor-compression refrigeration. Among all the EC materials, relaxor terpolymer P(VDF-TrFE-CFE) has been demonstrated as a promising candidate owing to its large EC effect and superior thermal stability. However, for the terpolymer, the EC strength (represented by EC temperature change under unit electric field (ΔT/E)) is still far from being satisfactory, which limits the mass application of terpolymer as a viable cooling medium in civil applications. Here, an effective method is employed to induce edge-on lamellae into the terpolymer to enhance the EC strength. Owing to the dipolar moments in the edge-on lamellae, which could be rotated more easily in the out-of-plane direction by the electric field, the treated terpolymer with edge-on lamellae exhibits a much enhanced EC strength of 0.13 K m−1 MV−1. Further exploration also shows a significantly decreased coercive field in the treated terpolymer due to the induced edge-on lamellae, and hence larger dipolar-entropy change could be generated at a modest electric field. The results indicate that a relaxor-like β-phase may also contribute to the enhanced polarizability. More importantly, the terpolymer with edge-on lamellae exhibits high thermal stability within a broad temperature range near room temperature. This work emphasizes the critical role of crystal structure on the macroscopic properties of electrocaloric polymers.

Objective To explore the effect of astragaloside IV in promoting bone development by promoting the proliferation of precartilaginous stem cells. Methods To co-cultured the cells from the resting chondrocyte of growth plate and LaCroix of 24-hours old rats,and identified by FGFR-3 staining. Choosing astragaloside IV induce precartilaginous stem cells cultured in vitro, using Collagen type Ⅱ monoclonal antibody staining and MTT to test cell biological characteristics. Four 4 weeks old SD rats were selected and divided into an experimental group and control group, 24 rats in each group. The rats in the experimental group were injected with astragalus injection in a dose of 8.0g / kg once a day. The rats in the other group were injected with the same amount of normal saline. The 3rd and 5th week after feeding, 12 rats were killed, and the tibial length was measured by vernier caliper.Rusults The FGFR-3 staining was positive, which proved that the cultured cells were precartilaginous stem cells. Collagen typeⅡmonoclonal antibody staining is positive and the OD value detected by MTT test was higher, after astragaloside IV induced the precartilaginous stem cells. After astragaloside IV injection, the tibial length of experimental group measured by vernier caliper was significantly higher than that of the control group.Conclusion astragaloside IV can promote the proliferation and biological characteristics of precartilaginous stem cells, and then promote bone development.

A novel technique, called augmented whole-body scanning via magnifying PET (AWSM-PET), that improves the sensitivity and lesion detectability of a PET scanner for whole-body imaging is proposed and evaluated. A Siemens Biograph Vision PET/CT scanner equipped with one or two high-resolution panel-detectors was simulated to study the effectiveness of AWSM-PET technology. The detector panels are located immediately outside the scanner’s axial field-of-view (FOV). A detector panel contains ${2} \times {8}$ detector modules each consisting of ${32} \times {64}$ LSO crystals ( ${1.0} \times {1.0} \times {10.0}$ mm3 each). A 22Na point source was stepped across the scanner’s FOV axially to measure sensitivity profiles at different locations. An elliptical torso phantom containing $7\times9$ spherical lesions was imaged at different axial locations to mimic a multi-bed-position whole-body imaging protocol. Receiver operating characteristic (ROC) curves were analyzed to evaluate the improvement in lesion detectability by the AWSM-PET technology. Experimental validation was conducted using an existing flat-panel detector integrated with a Siemens Biograph 40 PET/CT scanner to image a torso phantom containing spherical lesions with diameters ranging from 3.3 to 11.4 mm. The contrast-recovery-coefficient (CRC) of the lesions was evaluated for the scanner with or without the AWSM-PET technology. Monte Carlo simulation shows 36%–42% improvement in system sensitivity by a dual-panel AWSM-PET device. The area under the ROC curve is 0.962 by a native scanner for the detection of 4 mm diameter lesions with 5:1 tumor-to-background activity concentration. It was improved to 0.977 and 0.991 with a single- and dual-panel AWSM-PET system, respectively. Experimental studies showed that the average CRC of 3.3 mm and 4.3 mm diameter tumors were improved from 2.8% and 4.2% to 7.9% and 11.0%, respectively, by a single-panel AWSM-PET device. With a high-sensitivity dual-panel device, the corresponding CRC can be further improved to 11.0% and 15.9%, respectively. The principle of the AWSM-PET technology has been developed and validated. Enhanced system sensitivity, CRC and tumor detectability were demonstrated by Monte Carlo simulations and imaging experiments. This technology may offer a cost-effective path to realize high-resolution whole-body PET imaging clinically.

This paper presents a new high-sensitivity PET geometry for high fidelity MRI-compatible PET breast imaging which can scan both breasts simultaneously and have: high sensitivity and resolution; compatibility with MR-breast imaged volume; complete visualization of both breasts, mediastinum and axilla; and a modular design. Whereas contemporary dedicated x-ray and molecular breast imaging devices only scan one breast at a time, this approach relies on an unconventional PET geometry, and is able to provide a PET field of view (FOV) larger than that from dedicated breast MRI. The system geometry is evaluated with GATE Monte Carlo simulations of intrinsic system parameters. Various sized lesions (4-6mm) having [6:1 to 4:1] lesion:background radioactivity ratios mimicking different biological uptake are simulated, strategically located throughout a volumetric anthropomorphic torso. Dedicated breast PET (dbPET) imaging is compared with contemporary clinical PET. The dbPET system sensitivity is >6X greater than for contemporary whole-body PET. The novel, non-conventional system geometry allows for simultaneous dual-breast imaging, along with full medial and axillary imaging. Iteratively reconstructed full-volumetric images illustrate sharper visualization of 4mm lower uptake [4:1] lesions throughout the FOV compared with clinical PET. Image overlap between dedicated breast PET and MRI FOVs is excellent. Simulation results indicate clear superiority over conventional, high-sensitivity whole-body PET systems, as well as improved sensitivity over single-breast dbPET systems. This proposed system potentially facilitates both early detection and diagnosis, especially by increasing specificity of MRI, as well as visualizing tissue heterogeneity, monitoring therapeutic efficacy, and detecting breast cancer recurrence throughout the entire mediastinum.

Dielectric capacitors are always faced with high temperature in many application cases, so the applicability of high temperature is highly desired for dielectrics besides large energy storage density. Polyimide is a widely used engineering polymer with excellent thermotolerance and ceramic nanofillers with large aspect ratio are effective in improving the dielectric properties of polymer nanocomposite. In this work, PI nanocomposite films contained with BaTiO3 nanofibers prepared via electrospinning were fabricated by solution casting and thermal imidization process. The dielectric properties of the nanocomposites were investigated from room temperature to 200 °C. With the introduction of BaTiO3 nanofibers, the dielectric permittivity was enlarged with weak increase on dielectric loss in nanocomposites. The breakdown strength (550 kV/mm) as well as discharged energy density (5.82 J/cm3) was largely enhanced in BaTiO3/PI nanocomposite contained with 1 vol% nanofibers. Benefited from the decreased leakage current and improved thermal conduction induced by BaTiO3 nanofibers, the 1 vol% BaTiO3/PI nanocomposite also represented high energy efficiency and excellent thermal stability. The discharged energy density of above 2.1 J/cm3 and near 4 J/cm3 with efficiency larger than 90% are stable from room temperature to 150 °C and to 100 °C respectively. The high temperature applicability of the present material makes it much promising in fabricating dielectric energy storage devices applied in hot environment.

Electrocaloric effect (ECE) is much promising to realize high efficiency and environment friendly solution in solid cooling devices. Relaxor ferroelectrics are good candidates for the materials with high electrocaloric cooling power. In this paper, relaxor ferroelectric Ba(ZrxTi1-x)O3 (BZT, x = 0.2, 0.21, 0.22, 0.23) ceramics were prepared with their temperature change (ΔT) induced by the ECE and electrocaloric strength (ΔT/E) measured within broad temperature range. It is found that the BZT21 (x = 0.21) exhibits the largest ΔT of ∼4.67 K and a high ΔT/E value of ∼0.46 km/MV at 9.9 MV/m and 25 °C. BZT21 also exhibits apparent relaxor ferroelectric response, showing a very broad EC peak in the temperature interval between 15 °C and 50 °C. Moreover, the relationship between EC properties and relaxor features was analyzed by piezoresponse force microscopy test. The results reveal that more dispersed phase structures induce additional configurational entropy, which is in favor for the enhanced EC performance. The interplay and compromise between the kinetic and thermodynamic mechanisms of domain switching determines the optimal composition for the EC performances of the BZT ceramics.

The urgent demand for high-temperature dielectrics toward capacitive energy storage arises from numerous emerging harsh-environment high-temperature applications such as electric vehicles, aerospace power conditioning, downhole oil explorations. For these applications, it is imperative to enhance the discharge energy density of polymer-based dielectrics at elevated temperature. Herein, a trace composite approach is proposed and demonstrated. Two types of polyetherimides (PEIs)-based dipolar glasses are designed, synthesized and composited with trace amount of ultrafine Al2O3 nanoparticles. PEIs-based dipolar glasses with high Tg (~250 °C) and much enhanced electrical polarization are constructed by introducing dipolar groups (-CF3) and sulfonyl groups (-SO2-) with high dipolar moment (~4.30 D) in the polymer chains. The incorporation of ultrafine Al2O3 nanoparticles increases the electrical polarization and keeps low loss. The remarkable permittivity enhancement via the ultrafine filling could be ascribed to more active mobility of dipolar groups characterized by activation energy of movement and the correlation of arrangement of dipolar groups in the chains with this effect is also revealed. These results will contribute to deeply understanding and rationally designing high-performance polymer-based nanocomposites orienting to high-temperature electrical energy storage.

Polymer nanocomposite dielectrics with high energy density and low loss are major enablers for a number of applications in modern electronic and electrical industry. Conventional fabrication of nanocomposites by solution routes involves equilibrium process, which is slow and results in structural imperfections, hence high leakage current and compromised reliability of the nanocomposites. We propose and demonstrate that a nonequilibrium process, which synergistically integrates electrospinning, hot-pressing and thermal quenching, is capable of yielding nanocomposites of very high quality. In the nonequilibrium nanocomposites of poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) and BaTiO3 nanoparticles (BTO_nps), an ultrahigh Weibull modulus β of ∼30 is achieved, which is comparable to the quality of the bench-mark biaxially oriented polypropylene (BOPP) fabricated with melt-extrusion process by much more sophisticated and expensive industrial apparatus. Favorable phase composition and small cry...

Poly(vinylidene fluoride) (PVDF)-based polymers with excellent flexibility and relatively high permittivity are desirable compared to the traditional bulk ceramic in dielectric material applications. However, the low discharge efficiency (

Polymer nanocomposite dielectrics, composed of polymer matrices with high breakdown strength and nanofillers with high dielectric constant, can achieve outstanding energy density. However, the great difference of intrinsic surface properties between the polymer and nanofillers will lead to poor compatibility and thus damage the dielectric properties of the composites. Introducing a transition layer to the filler surface can effectively reduce the degree of mismatch. In this work, we use a “direct in situ polymerization” method to synthesize core–shell BaTiO3 nanoparticles (BTO_nps) with three types of stable and dense fluoro-polymer shells, e.g., poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA), poly(2,2,3,4,4,4-hexafluorobutyl methacrylate) (PHFBMA), and poly(1H,1H,7H-dodecafluoroheptyl methacrylate) (PDFHMA), and individually disperse them into the poly(vinylidene fluoride-co-hexafluoro propylene) (P(VDF-HFP)) matrix. Benefitting from the good interaction between the fluorine-containing segments in the shell polymer and the matrix segments, the dispersion of core–shell BTO_nps and their compatibility with P(VDF-HFP) are improved, which leads to a significant improvement in the dielectric properties of the nanocomposites. The results show that BTO@PDFHMA/P(VDF-HFP) composite exhibits an ultrahigh energy density of 16.8 J cm−3 at 609 MV m−1 with particle loading amount of 15 wt%, compared to 11.5 J cm−3 at 492 MV m−1 for a conventional solution blended BTO/P(VDF-HFP) composite. Meanwhile, the discharge efficiency is enhanced from ∼62 to ∼78%. It is elucidated that the core–shell strategy can achieve improved particle dispersion and dielectric properties. We consider that this simple method can well achieve the preparation of core–shell structures in dielectric nanocomposites.

Polymers with high dielectric strength and favorable flexibility have been considered promising materials for dielectrics and energy storage applications, while the achievable energy density (Ue) of polymer is rather limited by the intrinsic low dielectric constant and ferroelectric hysteresis. Polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VDF-TrFE-CFE)) with ultrahigh er of >50 is considered promising in achieving high Ue of polymer dielectrics. However, P(VDF-TrFE-CFE) only exhibits moderate Ue due to the early saturation of electrical polarization at low electric field. In this contribution, we show that, by blending P(VDF-TrFE-CFE) with polyvinylidene fluoride (PVDF), the early saturation of P(VDF-TrFE-CFE) is substantially suppressed, giving rise to concomitant enhancement of dielectric permittivity and breakdown strength. An ultrahigh energy density of 19.6 J/cm3 is thus achieved at ∼640 kV/mm, which is 1600% greater than Ue of the benchmark biaxially oriented polypropylene (BOPP...

An improved light-weight Compton camera exhibiting low power consumption was developed to be mountable on an unmanned helicopter to detect cesium radiation hot spots and confirm the decontamination effect of cesium-affected areas. An increase in the Ce:Gd3(Al,Ga)5O12 scintillator array from 4 × 4 to 8 × 8 and expansion of the interlayer distance enhanced the detection efficiency and angular resolution, respectively. Measurements were performed over the Ukedo riverbed in Namie, Fukushima Prefecture (Japan). The helicopter's flight path and speed were pre-programmed to lines interspaced by 5 and 10 m intervals and 1 m/s, respectively, facilitating measurements over areas of 65 × 60 m2 and 65 × 180 m2 at a height of 10 m for approximately 20 and 30 min, respectively. Results provided accurate ambient dose equivalent rate maps at a height of 1 m with an angular resolution corresponding to a position resolution of approximately 10 m from a height of 10 m. Hovering flights were executed over hot-spot ar...

Polymer nanocomposite dielectrics are of critical importance for a number of electrical and electronic applications. It is highly desirable to achieve high energy density at a low electric field. In this contribution, PVDF-based (or PVDF–TrFE–CFE based) nanocomposite films filled with BaTiO3@TiO2 nanofibers are cast from solutions. Topological-structure modulated polymer nanocomposites are assembled layer-by-layer with the as-cast films via a hot-pressing process. Modulation of the topological-structure induces substantial redistribution of the local electric field among the constituent layers, giving rise to enhanced electric polarization at a low electric field and increased breakdown strength. These synergistic effects lead to an ultrahigh energy density of ∼12.5 J cm−3 and a high discharge efficiency of ∼70% at 350 kV mm−1. High energy density at a low electric field is thus achieved by modulating the topological structure of polymer dielectric nanocomposites, which is of critical significance to make dielectric nanocomposites viable energy storage devices.

Composite polymer electrolyte is promising in future lithium-ion battery due to its high safety, easy-processing feature and electrochemical stability. However, it is still a great challenge to obtain the electrolyte with both low thickness and high conductivity. In this work, we synthesize a ~25 μm thin electrolyte membrane with the Li7La3Zr2O12-embedded polyacrylonitrile-based fiber as the 3D backbone and the in-situ polymerized gel electrolyte as the fillers. The electrolyte with the multi-dimensional lithium ion conducting channels exhibits a high conductivity of 1.60 × 10−3 S·cm−1 at 25 °C. The wide electrochemical window of 4.5 V vs. Li/Li+ enables the electrolyte to match with high voltage cathode materials. The Li||Li symmetric cell with the electrolyte shows a high cycling stability with more than 350 h at a current density of 0.1 mA·cm−2. In addition, the solid-state LiFePO4||Li full cell has a stable charge-discharge cycle at 25 °C. This thin electrolyte can be used in lithium-ion batteries to improve energy density. The method of preparing thin composite polymer electrolyte membrane can also be extended to other polymer-filler systems.

The electrocaloric effect (ECE) refers to reversible thermal changes of a polarizable material upon the application or removal of electric fields. Without a compressor or cooling agents, all-solid-state electrocaloric (EC) refrigeration systems are environmentally benign, highly compact, and of very high energy efficiency. Relaxor ferroelectric ceramics and polymers are promising candidates as EC materials. Here, synergistic efforts are made by composing relaxor Ba(Zr0.21 Ti0.79 )O3 nanofibers with P(VDF-TrFE-CFE) to make relaxor-relaxor-type polymer nanocomposites. The ECEs of the nanocomposites are directly measured and these relaxor nanocomposites exhibit, so far, the highest EC temperature change at a modest electric field, along with high thermal stability within a broad temperature range span to room temperature. The superior EC performance is attributed to the interfacial coupling between dipoles across the filler/polymer interfaces. The thermodynamics and kinetics of interfacial coupling are investigated in situ by piezoresponse force microscopy while the real-time evolution of interfacial coupling is simulated and visualized by phase-field modeling.

Due to the accident of Fukushima Daiichi Nuclear Power Plant, some areas were contaminated by released radioisotopes (mainly 137Cs and 134Cs). Effective decontamination is demanded to encourage eva...

Manipulating microstructures of composites in three dimensions has been a long standing challenge. An approach is proposed and demonstrated to fabricate artificial nanocomposites by controlling the 3D distribution and orientation of oxide nanoparticles in a polymer matrix. In addition to possessing much enhanced mechanical properties, these nanocomposites can sustain extremely high voltages up to ≈10 kV, exhibiting high dielectric breakdown strength and low leakage current. These nanocomposites show great promise in resolving the paradox between dielectric constant and breakdown strength, leading to ultrahigh electrical energy density (over 2000% higher than that of the bench-mark polymer dielectrics) and discharge efficiency. This approach opens up a new avenue for the design and modulation of nanocomposites. It is adaptable to the roll-to-roll fabrication process and could be employed as a general technique for the mass production of composites with intricate nanostructures, which is otherwise not possible using conventional polymer processing techniques.

In this project, we propose to investigate the feasibility of a novel technology that will bring both PET and ultrasound imaging to the patient bedside to support point-ofcare(PoC) molecular imaging applications. The system will comprise of a panel detector placed behind the patient and a maneuverable probe that consists of a PET detector and an ultrasound transducer. The probe can be moved around a region-of-interest in the patients’ body to collect both PET coincidence events and ultrasound signals. The location of the maneuverable probe relative to the back panel detectors is tracked in real-time as coincidence events are recorded. These events are used for list-mode image reconstruction in near realtime to provide visual feedback to the operator who can interactively control the probe to collect additional counts from the most critical locations and/or angles in order to dynamically optimize the image quality. To prove the concept, we developed a prototype that consists of a single channel SiPM(SensL FB30035) coupled to a 3.0 $\times$3.0$\times$20.0 mm$^{ 3}$ LSO crystal as the back detector. The maneuverable probe consists of an ultrasound transducer and a PMT(Hamamatsu H8500) coupled to 48$\times$48 LSO crystals of 1.0$\times$1.0$\times$10.0 mm$^{ 3}$ each. A robotic arm allows us to position the probe at arbitrary locations. Coincidence timing resolution of 470 ps FWHM has been achieved. We have implemented a GPUbased fully 3D list-mode Time-Of-Flight image reconstruction algorithm that can model the dynamically changing geometry of this PoC system. In this study, we report preliminary results from both actual experiments using this prototype and simulations using GATE. Detector modules with larger sensitive volume will be fabricated and tested to perform more imaging studies in order to explore the capability of this class of system.

Ferroelectric memories are endowed with high data storage density by nanostructure designing, while the robustness is also impaired. For organic ferroelectrics favored by flexible memories, low Curie transition temperature limits their thermal stability. Herein, a ferroelectric random access memory (FeRAM) is demonstrated based on an array of P(VDF‐TrFE) lamellae by self‐assembly. Written data shows enhanced thermal endurance up to 90 °C and undergoes 12 thermal cycles between 30 and 80 °C with little volatilization. The promoted thermal stability is attributed to pinning effect at interfaces between grain boundaries and lamellae, where charged domain walls and charged defects are coupled. These results provide a strategy for improving robustness of organic flexible FeRAMs, and reveal an attracting coupling effect between different phases of ferroelectric polymer.

Polyimide (PI) films with extremely high breakdown strength (451 kV/mm), energy density (5.2 J/cm3), and discharge efficiency (86.7%) at the room temperature are fabricated by simple solution casting method. Barium titanate (BaTiO3) nanoparticles are introduced into PI matrix, giving rise to enhanced dielectric permittivity (6.8) and low dielectric loss (0.012). Dielectric and energy storage performances of the BTO/PI nanocomposites are thoroughly investigated up to 200 °C. The breakdown strengths of both pure PI and BTO/PI nanocomposites decrease dramatically with the increase in the temperature, owing to the low thermal conductivity of PI and the consequent thermal runaway caused by the accumulation of Joule heat under high electric field. Despite of the enhanced electric displacement, BTO/PI nanocomposites exhibit low discharge energy density due to the substantially compromised breakdown strength induced by the BTO nanoparticles.

Large-aspect-ratio composite nanofibers with interior hierarchical interfaces are employed to break the adverse coupling of electric displacement and breakdown strength in flexible poly(vinylidene fluoride-hexafluoropropylene) nanocomposite films, a small loading of 3 vol% BaTiO3@TiO2 nanofibers gives rise to the highestenergy density (≈31.2 J cm(-3)) ever achieved in polymer nanocomposites dielectrics.