Mechanically Robust and Elastic Graphene/Aramid Nanofiber/Polyaniline Nanotube Aerogels for Pressure Sensors.

The preparation of graphene-based aerogels with excellent mechanical strength, elasticity, and compressibility is still a challenge. Herein, we demonstrate a robust, elastic, and lightweight graphene/aramid nanofiber/polyaniline nanotube (rGO/ANF/PANIT) aerogel that is prepared by mixing graphene oxide (GO), ANF, and PANIT dispersions, followed by thermal treatment at 90 °C, freeze-drying, and a low-temperature annealing process. The PANIT bonds the graphene sheets tightly, benefitting the formation of composite gels. The ANF tightly interconnects the graphene sheets and further reinforces the composite network framework significantly, hence endowing rGO/ANF/PANIT composite aerogels with robust mechanical property. The prepared aerogels present a low density of ∼12 mg cm-3, high conductivity, good resilience, and high compressibility. The rGO/ANF/PANIT aerogels as pressure sensors exhibit a high sensitivity of 1.73 kPa-1, low detection limit (40 Pa), wide detection range, and excellent compressive cycle stability, highlighting the promising applications in pressure-sensitive electrical devices, including medical health detection, wearable electronics, and intelligent packaging fields.

Study of the Off-Axis Fresnel Zone Plate of a Microscopic Tomographic Aberration.

A tomographic microscopy system can achieve instantaneous three-dimensional imaging, and this type of microscopy system has been widely used in the study of biological samples; however, existing chromatographic microscopes based on off-axis Fresnel zone plates have degraded image quality due to geometric aberrations such as spherical aberration, coma aberration, and image scattering. This issue hinders the further development of chromatographic microscopy systems. In this paper, we propose a method for the design of an off-axis Fresnel zone plate with the elimination of aberrations based on double exposure point holographic surface interference. The aberration coefficient model of the optical path function was used to solve the optimal recording parameters, and the principle of the aberration elimination tomography microscopic optical path was verified. The simulation and experimental verification were carried out utilizing a Seidel coefficient, average gradient, and signal-to-noise ratio. First, the aberration coefficient model of the optical path function was used to solve the optimal recording parameters. Then, the laminar mi-coroscopy optical system was constructed for the verification of the principle. Finally, the simulation calculation results and the experimental results were verified by comparing the Seidel coefficient, average gradient, and signal-to-noise ratio of the microscopic optical system before and after the aberration elimination. The results show that for the diffractive light at the orders 0 and ±1, the spherical aberration W040 decreases by 62-70%, the coma aberration W131 decreases by 96-98%, the image dispersion W222 decreases by 71-82%, and the field curvature W220 decreases by 96-96%, the average gradient increases by 2.8%, and the signal-to-noise ratio increases by 18%.

Mechanically strong multifunctional three-dimensional crosslinked aramid nanofiber/reduced holey graphene oxide and aramid nanofiber/reduced holey graphene oxide/polyaniline hydrogels and derived films.

To endow high mechanical strength and thermal stability aramid nanofibers (ANF) with novel functionality will lead to great applications. Herein, a strategy to generate covalent bonds among components towards obtaining uniform ANF/reduced holey graphene oxide (ANF/rHGO) and ANF/rHGO/polyaniline (ANF/rHGO/PANI) hydrogels with high mechanical properties is proposed through solvent exchange gelation and subsequent hydrothermal treatment. The as-prepared ANF/rHGO and ANF/rHGO/PANI hydrogels demonstrate excellent recoverability at high compressive strength of 20.2 and 13.8 kPa with a strain of 34.4% and 30.6%, respectively, compared to a recoverability of 92.5% at a strain of ∼20% for ANF hydrogels. Moreover, ANF/rHGO and ANF/rHGO/PANI aerogels possess fast and high oil absorption capacity of 38.9-64.1 g g-1 and 24.5-44.0 g g-1, respectively. ANF/rHGO and ANF/rHGO/PANI films obtained after vacuum-drying exhibit a high tensile strength of 121.4 and 95.5 MPa, respectively. Additionally, ANF/rHGO/PANI thin films present good selective absorption of visible light by controlling the doping level of PANI. ANF/rHGO/PANI aerogel films prepared by freeze-drying are assembled into flexible solid-state symmetric supercapacitors and deliver a favorable specific capacitance of 200 F g-1, a desirable capacitance retention of 98.9% after 2500 mechanical bending cycles and an approximately 100% capacitance retention even after keeping tensile force for 15 h. The as-prepared hydrogels, aerogels and derived films with such excellent performances are promising for applications in oil pollution removal, optical filters and flexible load-bearing energy storage devices.

Research and Application of Several Key Techniques in Hyperspectral Image Preprocessing.

This paper focuses on image segmentation, image correction and spatial-spectral dimensional denoising of images in hyperspectral image preprocessing to improve the classification accuracy of hyperspectral images. Firstly, the images were filtered and segmented by using spectral angle and principal component analysis, and the segmented results are intersected and then used to mask the hyperspectral images. Hyperspectral images with a excellent segmentation result was obtained. Secondly, the standard reflectance plates with reflectance of 2 and 98% were used as a priori spectral information for image correction of samples with known true spectral information. The mean square error between the corrected and calibrated spectra is less than 0.0001. Comparing with the black-and-white correction method, the classification model constructed based on this method has higher classification accuracy. Finally, the convolution kernel of the one-dimensional Savitzky-Golay (SG) filter was extended into a two-dimensional convolution kernel to perform joint spatial-spectral dimensional filtering (TSG) on the hyperspectral images. The SG filter (m = 7,n = 3) and TSG filter (m = 3,n = 4) were applied to the hyperspectral image of Pavia University and the quality of the hyperspectral image was evaluated. It was found that the TSG filter retained most of the original features while the noise information of the filtered hyperspectral image was less. The hyperspectral images of sample 1-1 and sample 1-2 were processed by the image segmentation and image correction methods proposed in this paper. Then the classification models based on SG filtering and TSG filtering hyperspectral images were constructed, respectively. The results showed that the TSG filter-based model had higher classification accuracy and the classification accuracy is more than 98%.

Arbitrary deformable and high-strength electroactive polymer/MXene anti-exfoliative composite films assembled into high performance, flexible all-solid-state supercapacitors.

Flexible all-solid-state supercapacitors (ASSSs) are excellent energy storage devices for portable/wearable electronics, although the development of an excellent comprehensive performance film electrode for the extraordinary flexible ASSSs still faces a great challenge. Here, bendable, foldable and anti-exfoliative Ti3C2Tx MXene-based films utilized as supercapacitor electrodes are reported. Polyaniline/Ti3C2Tx composites (i-PANI@Ti3C2Tx) were prepared by in situ oxidant-free polymerization of aniline on Ti3C2Tx nanosheets with p-phenylenediamine (PPD) as an initiator. Lignosulfonate (Lig) and Ti3C2Tx were constructed into a compact composite (Lig@Ti3C2Tx) film based on the hydrogen bonds formed between Lig and Ti3C2Tx. The Lig@Ti3C2Tx/i-PANI@Ti3C2Tx(5/5) hybrid film was produced by vacuum-assisted filtration of the mixed two composite dispersions. The as-prepared films can be arbitrarily deformed (such as bending and folding). They show high tensile strength and vertical-plane (the plane of film) tensile strength with 33.2 and 0.28 MPa for the i-PANI@Ti3C2Tx film, 75.4 and 0.77 MPa for the Lig@Ti3C2Tx film, and 53.7 and 0.58 MPa for the Lig@Ti3C2Tx/i-PANI@Ti3C2Tx(5/5) film (those of Ti3C2Tx film are 17.4 and 0.21 MPa), respectively. The enhanced vertical-plane tensile strength of the as-prepared composite films indicates that the large binding force generated between the Ti3C2Tx nanosheets can effectively prevent the exfoliation of films. The electrodes of the as-prepared i-PANI@Ti3C2Tx, Lig@Ti3C2Tx and Lig@Ti3C2Tx/i-PANI@Ti3C2Tx(5/5) films assembled into symmetric flexible ASSSs can deliver excellent specific capacitances of 310 F g-1 (∼1001 F cm-3), 271 F g-1 (∼881 F cm-3) and 295 F g-1 (∼959 F cm-3), respectively. In addition, the corresponding supercapacitors exhibit ultrahigh energy densities of 34.8, 30.6 and 33.3 W h L-1, respectively. It is expected that the as-prepared MXene-based films can be applied in various fields, such as electromagnetic-interference shielding and batteries. Furthermore, the as-prepared flexible ASSSs can be practically used as a wearable energy storage device.

Synthesis of morphology-tunable electroactive biomass/graphene composites using metal ions for supercapacitors.

Tannic acid (TA) is a natural polyphenolic biomass, which shows high electro-activity and can be considered for supercapacitor applications. However, the negligible electronic conductivity of TA hinders its direct use as an electrode. In order to achieve the electrochemical activity of TA, herein, a three-dimensional porous TA/graphene composite (TAG) is prepared by mixing TA with graphene oxide (GO) via hydrothermal assembly, and various structural composites are realized by adding metal ions into the system before hydrothermal treatment. Metal ions can chelate with TA molecules and coordinate with GO via electrostatic interactions. As a result, a uniform and well-defined three-dimensional porous network (TAGNi), a regularly arranged scale-like microstructure (TAGCu) and a flower-like structure (TAGFe) are achieved by introducing Ni2+, Cu2+ and Fe3+, respectively. The as-prepared TAG, TAGNi, TAGCu and TAGFe electrodes exhibit a high specific capacitance of 373.6, 412.4, 460.4 and 429.4 F g-1 at 1 A g-1, respectively, and excellent cycling stability. The TAG, TAGNi, TAGCu and TAGFe assembled symmetric supercapacitors display a favorable energy density of 14.76, 16.76, 19.13 and 17.6 W h kg-1 at 300 W kg-1, respectively. The morphology-tunable TA/graphene composites with excellent electrochemical performance are promising for renewable energy storage device applications.

Joint clustering with correlated variables.

Traditional clustering methods focus on grouping subjects or (dependent) variables assuming independence between the variables. Clusters formed through these approaches can potentially lack homogeneity. This article proposes a joint clustering method by which both variables and subjects are clustered. In each joint cluster (in general composed of a subset of variables and a subset of subjects), there exists a unique association between dependent variables and covariates of interest. To this end, a Bayesian method is designed, in which a semi-parametric model is used to evaluate any unknown relationships between possibly correlated variables and covariates of interest, and a Dirichlet process is utilized to cluster subjects. Compared to existing clustering techniques, the major novelty of the method exists in its ability to improve the homogeneity of clusters, along with the ability to take the correlations between variables into account. Via simulations, we examine the performance and efficiency of the proposed method. Applying the method to cluster allergens and subjects based on the association of wheal size in reaction to allergens with age, we found that a certain pattern of allergic sensitization to a set of allergens has a potential to reduce the occurrence of asthma.

High-Performance Biomass-Based Flexible Solid-State Supercapacitor Constructed of Pressure-Sensitive Lignin-Based and Cellulose Hydrogels.

Employing renewable, earth-abundant, environmentally friendly, low-cost natural materials to design flexible supercapacitors (FSCs) as energy storage devices in wearable/portable electronics represents the global perspective to build sustainable and green society. Chemically stable and flexible cellulose and electroactive lignin have been employed to construct a biomass-based FSC for the first time. The FSC was assembled using lignosulfonate/single-walled carbon nanotubeHNO3 (Lig/SWCNTHNO3) pressure-sensitive hydrogels as electrodes and cellulose hydrogels as an electrolyte separator. The assembled biomass-based FSC shows high specific capacitance (292 F g-1 at a current density of 0.5 A g-1), excellent rate capability, and an outstanding energy density of 17.1 W h kg-1 at a power density of 324 W kg-1. Remarkably, the FSC presents outstanding electrochemical stability even suffering 1000 bending cycles. Such excellent flexibility, stability, and electrochemical performance enable the designed biomass-based FSCs as prominent candidates in applications of wearable electronic devices.

Metal-Organic Coordination Polymer to Prepare Density Controllable and High Nitrogen-Doped Content Carbon/Graphene for High Performance Supercapacitors.

Design and preparation of carbon-based electrode material with high nitrogen-doping ratio and appropriate density attract much interest for supercapacitors in practical application. Herein, three porous carbon/graphene (NCGCu, NCGFe, and NCGZn) with high doping ratio of nitrogen have been prepared via directly pyrolysis of graphene oxide (GO)/metal-organic coordination polymer (MOCP) composites, which were formed by reacting 4,4'-bipyridine (BPD) with CuCl2, FeCl3, and ZnCl2, respectively. As-prepared NCGCu, NCGFe and NCGZn showed high nitrogen doping ratio of 10.68, 12.99, and 11.21 at. %; and high density of 1.52, 0.84, and 1.15 g cm-3, respectively. When as-prepared samples were used as supercapacitor electrodes, NCGCu, NCGFe and NCGZn exhibited high gravimetric specific capacitances of 369, 298.5, 309.5 F g-1, corresponding to high volumetric specific capacitances of 560.9, 250.7, 355.9 F cm-3 at a current density of 0.5 A g-1, as well as good cycling stability, nearly 100% of the capacitance retained after 1000 cycles even at a large current density of 10 A g-1. It is expected that the provided novel strategy can be used to develop electrode materials in high performance energy conversion/storage devices.

Power of a reproducing kernel-based method for testing the joint effect of a set of single-nucleotide polymorphisms.

This study explored a semi-parametric method built upon reproducing kernels for estimating and testing the joint effect of a set of single nucleotide polymorphisms (SNPs). The kernel adopted is the identity-by-state kernel that measures SNP similarity between subjects. In this article, through simulations we first assessed its statistical power under different situations. It was found that in addition to the effect of sample size, the testing power was impacted by the strength of association between SNPs and the outcome of interest, and by the SNP similarity among the subjects. A quadratic relationship between SNP similarity and testing power was identified, and this relationship was further affected by sample sizes. Next we applied the method to a SNP-lung function data set to estimate and test the joint effect of a set of SNPs on forced vital capacity, one type of lung function measure. The findings were then connected to the patterns observed in simulation studies and further explored via variable importance indices of each SNP inferred from a variable selection procedure.

smcure: an R-package for estimating semiparametric mixture cure models.

The mixture cure model is a special type of survival models and it assumes that the studied population is a mixture of susceptible individuals who may experience the event of interest, and cure/non-susceptible individuals who will never experience the event. For such data, standard survival models are usually not appropriate because they do not account for the possibility of cure. This paper presents an R package smcure to fit the semiparametric proportional hazards mixture cure model and the accelerated failure time mixture cure model.

Semiparametric Accelerated Failure Time Partial Linear Model and Its Application to Breast Cancer.

Breast cancer is the most common non-skin cancer in women and the second most common cause of cancer-related death in U.S. women. It is well known that the breast cancer survival varies by age at diagnosis. For most cancers, the relative survival decreases with age but breast cancer may have the unusual age pattern. In order to reveal the stage risk and age effects pattern, we propose the semiparametric accelerated failure time partial linear model and develop its estimation method based on the P-spline and the rank estimation approach. The simulation studies demonstrate that the proposed method is comparable to the parametric approach when data is not contaminated, and more stable than the parametric methods when data is contaminated. By applying the proposed model and method to the breast cancer data set of Atlantic county, New Jersey from SEER program, we successfully reveal the significant effects of stage, and show that women diagnosed around 38s have consistently higher survival rates than either younger or older women.