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In this work, we developed a flexible and stretchable bending sensor that is made of graphene film decorated with dense pores and sealed with both polyethylene terephthalate (PET) and elastic rubber layers. The graphene film was laid on a PET substrate to disperse the stretching stress and then covered by another smooth PET layer for reducing shear force. Platinum-catalyzed silicone rubber was employed for protecting the graphene film and providing the stretchability of the whole structure. Properties of the graphene film were investigated through the scanning electron microscope (SEM), Raman spectrometer, X-ray diffraction, and mechanical evaluations. Results indicate that the sensitivity of the proposed bending sensor reaches 1.092 mV/deg with excellent linearity and the resolution achieves 1°. Satisfactory repeatability was also observed with a mean square error of 0.105 of ignorable distortion after 1000 cycles of bending. On-human experiments verified that the bending sensor could accurately sense the bending angles of different human joints without additional structural modification. The results lead us to believe that the proposed method is a promising path for fabricating flexible and stretchable sensors with high performance and stability.

This article deals with the set-membership state estimation problem for a class of artificial neural networks subject to time-delays and mixed malicious attacks. Both Denial-of-Service (DoS) and deception attacks are taken into consideration. The objective of the addressed problem is to design the state estimation algorithm for the artificial neural networks under investigation in spite of the existence of the malicious mixed attacks. By means of the set-membership approach in combination with certain convex optimization algorithm, the sufficient condition is established for the existence of the desired state estimator in terms of the solvability of a recursive matrix inequality. The resulting state estimation error is confined within certain pre-specified ellipsoidal region. An optimization problem is then formulated with the purpose of seeking the filtering parameters guaranteeing the locally optimal performance. Finally, the developed theoretical results are verified via an illustrative numerical example.

Surface acoustic wave (SAW) humidity sensors promise broad prospects for Internet of Things (IoT) applications due to the advantages of low cost, portability, and high sensitivity. However, previous researches mainly focused on developing SAW devices with higher resonant frequencies, or using new sensing materials to improve the performance of SAW humidity sensors. Few researches studied the specific response mechanism of SAW humidity sensors, which restricted further development of the sensors. In this paper, the sensing mechanism of a graphene oxide (GO) film-based SAW humidity sensor is thoroughly studied by investigating the mechanical and electrical parameters of the uniform GO membrane at different relative humidity (from 10% RH to 90% RH). After taking these parameters into consideration for the mechanism analysis, we quantitatively indicate that the mass loading (~800 ppm) and viscoelastic effects (~60 ppm) are the primary and secondary influence factors of the sensor’s humidity response respectively, while the acoustoelectric interaction has little effect on the sensitivity. [2020-0024]

Graphene oxide (GO), an important chemical precursor of graphene, can stably disperse in aqueous surrounding and undergo aggregation as metal cations introduced. The usual instability of GO with ions is caused by the shielding effect of ions and crosslinking between GO and ions. However, the dynamic stability of GO under ions exchange still remains unclear. Here, we investigated the dynamic dispersion stability of GO with metal ions and observed a redispersion behavior in concentrated Fe3+ solution, other than permanent aggregation. The exchange with Fe3+ ions drives the reversion of Zeta (ζ) potential and enables the redispersion to individual GO-Fe3+ complex sheets, following a dynamic electric double layer (EDL) mechanism. It is found that the specifically strong electrostatic shielding effect and coordination attraction between Fe3+ and functional oxygen groups allows the selective redispersion of GO in concentrated Fe3+ solution. The revealed dynamic dispersion stability complements our understanding on the dispersive stability of GO and can be utilized to fabricate graphene-metal hybrids for rich applications.

To analyze the relationship between brain MRI, clinical symptoms, and cerebrospinal fluid (CSF) and to provide a reference for early diagnosis of anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis. A total of 62 patients with anti-NMDAR encephalitis in Zhengzhou, China (2016–2018) were observed and registered prospectively. First, we analyzed the characteristics of clinical symptoms. Second, according to the disease duration, patients were divided into two groups, and then we analyzed the CSF features. In addition, they were divided into two groups according to the brain MRI, and then the CSF features were analyzed. Finally, the characteristics of cerebrospinal fluid in patients with seizure as the initial symptom were analyzed. Seizure presents as the initial symptom in 14 patients (22.5%), including 11 males (78.57%). The proportion and concentration of CSF total protein abnormalities in the early stage group were significantly higher than those in the middle and late group (P < 0.05). The total protein concentration in the abnormal brain MRI group was significantly higher than that in the normal MRI group (P < 0.05). Anti-NMDAR encephalitis should be suspected, when male patients complain of seizure as an initial symptom and have simultaneously had headaches or fever prior to onset. The sensitivity of anti-NMDAR antibody is higher in CSF than in serum. Total CSF protein is more prone to elevation in the middle and late stages of anti-NMDAR encephalitis. Brain MRI abnormalities with anti-NMDAR encephalitis are related to the total protein concentration of CSF, which may be related to the disease duration.

Highly porous graphene aerogels (GAs) demonstrate extensive applications in damping blocks, thermal insulation, sensors, catalyst carriers and energy storage because of their ultralow density, superelasticity and functional versatility. These properties have been regulated by topological structural design and composite of materials, but the effect of the structural unit on the properties of GA has not been reported. Herein, highly porous GAs with excellent mechanical performances and improved adsorption capacities have been prepared by a freezing-drying process. Ultra-flyweight (ρ

We experimentally measure the contributions of beam distortion and wandering to OAM modal coupling through a random turbulent medium. The inter-modal power coupling further increases under turbulent-medium-induced beam distortions in comparison with the beam-wandering-only cases.

We experimentally demonstrate a 2.25-Gbit/s DPSK free-space optical link that resilience to turbulence-induced modal coupling loss. The measured average mixing loss is ~14.6-dB less than a single-mode-fiber-coupled system based on 200 random turbulence realizations.

We experimentally demonstrate a 6-Gbit/s 16-QAM pilot-assisted self-coherent free-space optical link with enhanced misalignment tolerance. BER performance below the 7% FEC threshold can be achieved for up to 0.13° angular- or 9-mm lateral misalignments.

We experimentally generate a Laguerre-Gaussian (LG ℓ , p ) beam with tunable spatial indices (LG0,0, LG0,1, LG+1,0, and LG+1,1) using integrated circular antenna arrays. A 10-Gbit/s free-space QPSK link carried by the generated LG beam is demonstrated.

We experimentally demonstrate the generation of a space-time pulse in free-space after 1-m multi-mode fiber propagation. The generated space-time pulse has reduced diffraction and a tunable group velocity from 1.0042c to 0.9967c.

We experimentally demonstrate the probing of turbulence along the propagation direction by transmitting multiple complementary pairs of longitudinally structured beams between a single transmitter/receiver aperture pair. The results show probing errors could be reduced by >~25% when using pairs of beams compared to using only one type of beam.

A solvent-free thermoplastic forming processing of graphene materials is invented by polymer intercalation from graphene oxide precursor.The correlation between interlayer spacing and thermoplastic forming capability of polymer-intercalated graphene oxide solid is uncovered.The multi-scale forming of graphene materials from Gaussian curved shapes to surface relief patterns with size precision down to 360 nm is realized. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00755-8., The processing capability is vital for the wide applications of materials to forge structures as-demand. Graphene-based macroscopic materials have shown excellent mechanical and functional properties. However, different from usual polymers and metals, graphene solids exhibit limited deformability and processibility for precise forming. Here, we present a precise thermoplastic forming of graphene materials by polymer intercalation from graphene oxide (GO) precursor. The intercalated polymer enables the thermoplasticity of GO solids by thermally activated motion of polymer chains. We detect a critical minimum containing of intercalated polymer that can expand the interlayer spacing exceeding 1.4 nm to activate thermoplasticity, which becomes the criteria for thermal plastic forming of GO solids. By thermoplastic forming, the flat GO-composite films are forged to Gaussian curved shapes and imprinted to have surface relief patterns with size precision down to 360 nm. The plastic-formed structures maintain the structural integration with outstanding electrical (3.07 × 105 S m−1) and thermal conductivity (745.65 W m−1 K−1) after removal of polymers. The thermoplastic strategy greatly extends the forming capability of GO materials and other layered materials and promises versatile structural designs for more broad applications. Graphical abstract Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00755-8.

To assess carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA19-9), platelet distribution width (PDW), neutrophil-to-lymphocyte ratio (NLR), and platelet-lymphocyte ratio (PLR) for gastric cancer's (GC) diagnostic efficiency, and the use of receiver operating characteristic curves (ROC) combined with logistic regression to evaluate multi-index combination's diagnostic value of GC. 773 GC patients' clinical data were retrospectively collected in the Weihai Municipal Hospital, affiliated hospital of Shandong University from April 2018 to May 2021, and selected 2368 healthy physical examination patients during the same period as the control group. A total of 3141 samples was included in this study, including 773 cases in the GC group and 2368 cases in the healthy physical examination group. The results of the overall comparison between groups showed that apart from gender, the age differences, CEA, CA19-9, PDW, NLR, and PLR were statistically significant (P .001). Spearman ranks correlation analysis's results showed that CA19-9, CEA, PLR, and NLR were correlated with GC patients' clinical-stage positively, and the correlation coefficients r was 0.249, 0.280, 0.252, 0.262 (all P .001), and PDW was correlated with the clinical stage negatively (r = -0.186, P .001). The ROC curve analysis results of CEA, CA19-9, PDW, NLR and PLR showed that CEA's diagnostic cutoff value for GC was 3.175 (area under the curve [AUC] = 0.631, 95% CI: 0.606-0.655, P .001), the CA19-9's diagnostic cutoff value is 19.640 (AUC = 0.589, 95% CI: 0.563-0.615, P .001), PDW's diagnostic cutoff value is 15.750 (AUC = 0.799, 95% CI: 0.778-0.820, P .001), NLR's diagnostic cutoff value was 2.162 (AUC = 0.699, 95% CI: 0.675-0.721, P .001), and PLR's diagnostic cutoff value was 149.540 (AUC = 0.709, 95% CI: 0.688-0.732, P .001). The area under the ROC curve for the combined diagnosis of GC with 5 indicators was 0.877 (95% CI: 0.860-0.894, P .001), which was better than a single indicator (P .05). The diagnostic efficiency of combined detection of CEA, CA19-9, PDW, NLR, and PLR is better than that of single index detection alone, which can reduce the misdiagnosis rate of GC effectively.

Discrete element (DE) model has a great feasibility in modelling the microstructural behaviours of adhesive composite joints. However, it demands a sophisticated calibration process to determine microscale bond parameters, which involves massive efforts in both experimental and numerical investigations. This work developed a novel calibration strategy based on DE models and genetic expression programming (GEP) approach for predicting the behaviours of hybrid composite joints encompassing the material nonlinearity, large ductile deformation and multiple fracture modes. In the developed strategy, both the bulk and interlaminar-like properties of ductile adhesives were concerned to suit various joint configurations. GEP modelling was performed based on the datasets from virtual DE experiments. Symbolic regression models were subsequently developed to facilitate the parameters determination. A series lab tests were conducted to validate the numerical results. It shows that the calibrated DE model can adaptively simulate the featured behaviours of both the ductile adhesive and composite joints with different configurations well in most examined occasions. Therefore, it could be suggested to generalize the developed strategy in the development of other DE models for saving the massive efforts in the calibration process of microstructural parameters.

We experimentally generate an orbital-angular-momentum (OAM) beam with a tunable mode order over a range of wavelengths utilizing an integrated broadband pixel-array OAM emitter. The emitter is composed of a 3-to-4 coupler, four phase controllers, and a mode convertor. An optical input is split into four waveguides by the coupler. Subsequently, the four waveguide fields are coherently combined and transformed into a free-space OAM beam by the mode convertor. By tuning the phase delay Δ φ between the four waveguides using the integrated phase controllers, the OAM order of the generated beam could be changed. Our results show that (a) a single OAM beam with a tunable OAM order ( ℓ = − 1 or ℓ = + 1 ) is generated with the intermodal power coupling of < − 11 d B , and (b) in a wavelength range of 6.4 nm, a free-space link of a single 50 Gbaud quadrature-phase-shift-keying (QPSK) channel carried by the tunable OAM beam is achieved with a bit error rate below the forward-error-correction threshold. As proof of concept, a 400 Gbit/s OAM-multiplexed and WDM QPSK link is demonstrated with a ∼ 1 − dB OSNR penalty compared with a single-beam link.

Piezoelectric cantilevers promise broad prospects for gas sensing and biosensing due to the high sensitivity and fast response. The strong correlation between the resonant frequency and sensitivity leads to numerous cantilever-based sensors using the high-order flexural mode to realize higher absolute sensitivity. However, experiment results show that the relative sensitivity of the sensors decreases with the increase of the mode order. Herein, we explain the relative sensitivity degeneration of normal cantilevers with a modified coefficient of equivalent mass, and propose a cantilever-based humidity sensor using high-frequency mode driven by interdigital electrodes (IDEs) to enhance the relative sensitivity. Compared with the high-order mode excited by normal configuration (70.4 MHz), the high-frequency mode driven by IDEs (77.3 MHz) demonstrates an improved sensitivity around 39.2 Hz $\cdot $ cm2/ng (1.68x) at 10%–90% relative humidity. The sensitivity enhancement by IDEs is consistent with the result calculated by the modified coefficient. [2020-0055]

Air stable, lightweight, and electrically conductive carbon-based films are highly desired for flexible electronic devices and products. Graphene film, a macroscopic assembly of individual graphene sheets, holds great potential to replace conventional brittle pyrolytic carbon film due to the excellent electrical transport property and flexibility. However, the electrical conductivity of graphene film is still inferior to metallic conductors, usually unstable in air as doped. We chose metal chloride (MoCl5) as air stable dopant and fabricated doped graphene film with well-controlled intercalation structure. The MoCl5 modified graphene film shows record high electrical conductivity of 1.73 × 107 S m−1, record high mobility of 2190.47 cm2 V−1 s−1, remarkable specific electrical conductivity exceeding benchmark metals (e.g., Au, Ag, Cu), and ultralow temperature coefficient of resistance (1.4 × 10−4 K−1). Importantly, the electrical conductivity and overall structure of MoCl5 intercalated films are exceptional stable in atmospheric environment, enabling wide applications in electronic devices, electromagnetic interference, and energy storage.

The accurate and fast diagnosis of transformer winding deformation faults is of significance to power suppliers and utilities. An improved winding mechanical deformation fault classification method is proposed. In this study, the transformer frequency response data is used to draw polar plots, and then its texture features are extracted for fault classification. The classification model constructed by multiple support vector machines is successfully obtained and shows good classification effect. Besides, this article uses an improved genetic algorithm based on the Emperor-Selective mating scheme and catastrophic operation, to optimize the parameters of support vector machine. The feasibility and accuracy of the proposed method are verified with experimental data obtained from a model transformer, and the proposed method is demonstrated to exhibit better performance compared with the traditional method.

In this paper, we experimentally demonstrate the mitigation of atmospheric turbulence effects using phase patterns that apply the inverse transmission matrix for pre-compensation in the 200-Gbit/s free-space orbital angular momentum (OAM) multiplexed optical link. In this link, two OAM channels are multiplexed, each carrying a 100-Gbit/s quadrature-phase shift keying (QPSK) signal. In the uni-directional (forward) link, a combination of two OAM modes is generated using a designed phase pattern in each of the two channels. After the two channels are multiplexed, each OAM mode will carry the combination of signals from both channels. Such beams could perform the inverse function of turbulence-induced crosstalk. We explore the link performances including crosstalk and bit error rate (BER) under 6 different turbulence realizations with a Fried parameter of 1-mm. We find the following: (a) the inter-channel crosstalk is reduced by up to 21 dB; (b) the inter-channel crosstalk is below −10 dB for the 6 turbulence realizations when the compensation is applied; (c) a BER below the FEC limit could be realized for the 6 turbulence realizations with an optical signal-to-noise ratio (OSNR) of 16.8 dB for the uni-directional link with the compensation. Moreover, the post-compensation is also investigated for the two 100-Gbit/s OAM-multiplexed backward channels in the bi-directional link. For the backward channels, the phase patterns are used to mitigate turbulence-induced crosstalk at the receiver for backward channels, and the inter-channel crosstalk is reduced by up to 16 dB.

In this letter, we experimentally explore the limited-size aperture effects in an orbital-angular-momentum (OAM)-multiplexed free-space optical (FSO) data link for aerial platforms. 200-Gbit/s data transmission is demonstrated between a ground transmitter and a ground receiver via a flying, retro-reflecting unmanned-aerial-vehicle (UAV) over 100-m round-trip distance by multiplexing two OAM beams. Our results indicate that when the receiver aperture size is limited, both power loss and channel crosstalk would increase. With a receiver aperture diameter of >5 cm, bit error rate (BER) mostly below 3.8 × 10−3 has been achieved for both channels

TEMPO-mediated oxidation has been successfully used to prepare carboxylated chitin nanofibers (ChNFs) with purified chitins originating from the outer shells of crab and shrimp (α-form) or tubeworm (β-form). However, the method for obtaining carboxylated ChNFs with squid pen chitin (hydrated β-form) has not been developed yet. It might be due to the existence of the small amount of partial deacetylation (DD ≈ 9%) in the squid pen β-chitins. Herein, ultrafine (2–4 nm in width and several micrometers in length) and carboxylated β-ChNFs were fabricated directly from the squid pen with simultaneously removing of protein, CaCO3 and other non-chitin components by one-step oxidation procedure using ammonium persulfate (APS) and followed ultrasonic disintegration under acid conditions. When 45 wt% APS was used to react with squid pen, the carboxylate content of ChNFs reaches 0.802 mmol/g. Therefore, the β-ChNFs with anionically charged groups (COO−) can be dispersed stably in aqueous solution under basic conditions. Meanwhile, thus-obtained β-ChNFs aqueous solution even with very low concentration (0.8%) can be transformed to transparent, robust and moldable hydrogels by gas coagulation of acetic acid.

We experimentally demonstrate a 4-Gbit/s 16-QAM pilot-assisted, self-coherent, and turbulence-resilient free-space optical link using a photodetector (PD) array. The turbulence resilience is enabled by the efficient optoelectronic mixing of the data and pilot beams in a free-space-coupled receiver, which can automatically compensate for turbulence-induced modal coupling to recover the data’s amplitude and phase. For this approach, a sufficient PD area might be needed to collect the beams while the bandwidth of a single larger PD could be limited. In this work, we use an array of smaller PDs instead of a single larger PD to overcome the beam collection and bandwidth response trade-off. In the PD-array-based receiver, the data and pilot beams are efficiently mixed in the aggregated PD area formed by four PDs, and the four mixing outputs are electrically combined for data recovery. The results show that: (i) either with or without turbulence effects ( D / r 0 = ∼8.4), the 1-Gbaud 16-QAM signal recovered by the PD array has a lower error vector magnitude than that of a single larger PD; (ii) for 100 turbulence realizations, the pilot-assisted PD-array receiver recovers 1-Gbaud 16-QAM data with a bit-error rate below 7% of the forward error correction limit; and (iii) for 1000 turbulence realizations, the average electrical mixing power loss of a single smaller PD, a single larger PD, and a PD array is ∼5.5 dB, ∼1.2 dB, and ∼1.6 dB, respectively.

Planar metasurface-based quarter wave plates (QWPs) have significant advantages over conventional devices in terms of compactness, flexibility, and simplicity of manufacture; however, they offer a relatively narrow operational bandwidth. A broadband terahertz achromatic QWP is realized in the 0.68–1.48 THz spectral region in this work, which consists of several separate metasurface layers of dielectric elliptic pillars stacked together with various rotation angles. Meanwhile, an improved simulated annealing method is proposed, which introduces the evolutionary strategies to optimize the distinct fundamental microstructural unit cells, and the running speed is greatly increased. Furthermore, the proposed multi-layers metasurface may pave the way for arbitrary polarization control of incident waves and be ideally suited for application by virtue of subwavelength thickness in the other frequency bands as well.

In free-space optical (FSO) communications, there are scenarios (e.g., from a ground station to a drone/airplane) in which: (i) the transmitter (Tx) can have a relatively large aperture whereas the receiver (Rx) aperture should preferably be much smaller, and (ii) the distance between the Tx and Rx can vary such that beam divergence will cause a variation in the recovered signal power. In such cases, transmission using a fundamental Gaussian beam can be significantly degraded due to beam truncation caused by a limited-size Rx aperture. Here, we experimentally demonstrate a 1-Gbit/s on-off keying (OOK) FSO transmission link using a structured “pin-like” beam with a limited-size Rx aperture at various distances. The pin-like beam is generated by passing a Gaussian beam through an “Airy-type” phase pattern in the radial direction. When propagating, this structured beam first narrows and then tends to maintain its narrow beam size over a fairly wide range of distances. In comparison to its Gaussian counterpart, our experimental results show that the pin-like beam has ∼13 to 8 dB less power loss at distances ranging from 0.45 m to 0.8 m with an Rx aperture diameter of 1 mm. Moreover, we simulate the propagation of the pin-like beam and show its relatively lower power loss for a wide distance variation in a longer link (e.g., ∼1 km) with a limited-size Rx aperture. Furthermore, our results show that the pin-like beam can have a wider range of low-power-loss distances than a Gaussian beam that is focused to a given distance.

In general, there are different, relatively independent forms of orbital angular momenta at a given propagation distance, which might exhibit different dynamic spatial characteristics. One type involves a beam with a helical phasefront that rotates around its own beam center, such as a Laguerre–Gaussian (LG) beam with an azimuthal index not equal to zero. The other one is a Gaussian-like beam dot that revolves around a central axis. Here, we experimentally demonstrate the generation of a dynamic spatiotemporal (ST) structured beam that simultaneously exhibits both rotation and revolution at a given propagation distance. Nine Kerr frequency comb lines are coherently combined, each carrying a designed superposition of multiple LG modes containing one unique ℓ value and multiple p values. Experimental results show that the mode purity of the reconstructed revolving and rotating LG30 beam is ∼89% when both the beam waist and revolving radius (R) are 0.4 mm. Moreover, we explore the effects of the number of frequency comb lines and the R value on the mode purity of the generated ST beam. Consequently, we find that a higher mode purity can be achieved by involving more frequency comb lines or reducing the R.