Preparation of pH-Responsive Films from Polyvinyl Alcohol/Agar Containing Cochineal for Monitoring the Freshness of Pork.

This study reported the production of pH-responsive films based on 8 wt% polyvinyl alcohol solution/0.2 wt% agar solution incorporated with cochineal-loaded starch particles (CSN) (2, 4, 6 and 8 wt% on agar basis) by a casting process. Results revealed that CSN presented obvious color changes over the pH range of 2-12. FTIR, XRD spectra and SEM micrographs presented that the incorporation of CSN formed new hydrogen bonds with a matrix and a tighter network structure. A certain improvement was observed in the color stability, swelling index and functional properties (antimicrobial and antioxidant activities) but water solubility, water vapor permeability and water contact angle of the pH-responsive films were decreased by the addition of CSN. The release of cochineal was a rate-limiting step following the Korsmeyer-Peppas model. The agar/polyvinyl alcohol film containing 6% CSN (PVA/GG-6) exhibited the best sensitivity for ammonia detection and its limit of detection was 35.4 ppm (part per million) for ammonia. The application trials showed that the PVA/GG-6 film presented different color changes for pork freshness. Hence, these pH-responsive films can be used as potential packaging materials for tracking the freshness of protein-rich fresh food in a non-destructive way.

Novel colorimetric films based on polyvinyl alcohol/sodium carboxymethyl cellulose doped with anthocyanins and betacyanins to monitor pork freshness.

A novel colorimetric film was developed from polyvinyl alcohol/sodium carboxymethyl cellulose (PVA/CMC-Na, CPA) incorporated with anthocyanins (AHO) or betacyanins (BTA) or AHO and BTA mixtures (in the mass ratios of 2:2, 3:1, 1:3) for intelligent packaging. Fourier transform infrared (FTIR) and scanning electron microscope (SEM) illustrated that AHO/BTA were immobilized into CPA network and improved compatibility of PVA and CMC-Na. The incorporation of AHO/BTA increased the tensile strength (TS), elongation at break (EAB), thickness and water solubility (WS) of the sample but decreased the crystallinity and swelling index (SI) of the sample. Furthermore, the colorimetric films presented antioxidant activity besides antibacterial activity against Escherichia coli and Staphylococcus aureus. The colorimetric film incorporated with AHO and BTA at a mass ratio of 3:1 indicated different colors to represent the freshness of pork. The novel colorimetric film possesses great potential in intelligent packaging for monitoring the real-time freshness of pork products.

Recent Advances in pH-Responsive Freshness Indicators Using Natural Food Colorants to Monitor Food Freshness.

Recently, due to the enhancement in consumer awareness of food safety, considerable attention has been paid to intelligent packaging that displays the quality status of food through color changes. Natural food colorants show useful functionalities (antibacterial and antioxidant activities) and obvious color changes due to their structural changes in different acid and alkali environments, which could be applied to detect these acid and alkali environments, especially in the preparation of intelligent packaging. This review introduces the latest research on the progress of pH-responsive freshness indicators based on natural food colorants and biodegradable polymers for monitoring packaged food quality. Additionally, the current methods of detecting food freshness, the preparation methods for pH-responsive freshness indicators, and their applications for detecting the freshness of perishable food are highlighted. Subsequently, this review addresses the challenges and prospects of pH-responsive freshness indicators in food packaging, to assist in promoting their commercial application.

Dynamic Invariant-Specific Representation Fusion Network for Multimodal Sentiment Analysis.

Multimodal sentiment analysis (MSA) aims to infer emotions from linguistic, auditory, and visual sequences. Multimodal information representation method and fusion technology are keys to MSA. However, the problem of difficulty in fully obtaining heterogeneous data interactions in MSA usually exists. To solve these problems, a new framework, namely, dynamic invariant-specific representation fusion network (DISRFN), is put forward in this study. Firstly, in order to effectively utilize redundant information, the joint domain separation representations of all modes are obtained through the improved joint domain separation network. Then, the hierarchical graph fusion net (HGFN) is used for dynamically fusing each representation to obtain the interaction of multimodal data for guidance in the sentiment analysis. Moreover, comparative experiments are performed on popular MSA data sets MOSI and MOSEI, and the research on fusion strategy, loss function ablation, and similarity loss function analysis experiments is designed. The experimental results verify the effectiveness of the DISRFN framework and loss function.

Re-construction of a HPGe detector precise modeling for efficiency calibration.

High purity germanium (HPGe) detector is a preferred choice for determining the activity of the radioactive samples for nuclear diagnostics of Inertial Confinement Fusion (ICF) experiments. Although the amounts of the radiochemical sample are limited, activity measurement at a close distance between the detector window and the radioactive source is a feasible method. Efficiency calibration of gamma rays at a close distance from the surface of a HPGe detector is crucial. Considering the problem of the coincidence at a close distance, the alternative way is to construct a precise model of the HPGe detector and then to calculate efficiency accurately at an arbitrary distance from the surface of the HPGe detector using Monte Carlo method. In this paper, internal geometry and structure except for dead layers of the HPGe detector is obtained by X-ray radiography and 3D reconstruction. The optimal dead layers of the germanium crystal are determined by tracing the minimal sum squared residual (SSR) of gamma-ray efficiencies between calculations and measurements for standard planar sources. Nonhomogeneous distribution of the dead layer is supposed according to the inner structure on the Ge crystal. The final results show that the corrected model improves the accuracy of the calculated efficiencies.

An improved equivalent-input-disturbance approach for PMSM drive with demagnetization fault.

Closed-loop torque control system of permanent magnet synchronous motor (PMSM) drive is highly applied in industrial applications. However, high temperature and other external factors lead to permanent magnet (PM) demagnetization fault of the motor, which inevitably brings barriers to precise torque control. This paper presents a rejection method for demagnetization based on an improved equivalent-input-disturbance (EID) approach. A system model, which contains demagnetization fault, is first constructed. Then, an equivalent-input-demagnetization on the control input channel is used to describe the model. An improved EID approach is designed to reject the effect of the demagnetization fault. In particular, an improved sliding-mode observer rather than the Luenberger observer in a conventional EID theory is designed to estimate the equivalent-input-demagnetization. This greatly enhances the response speed and accuracy of the estimation and rejection, and then effectively improves the accuracy of torque tracking. Finally, the step change and the ramp change of a demagnetization are introduced into a hardware-in-the-loop experiment, separately. Comparisons with other methods show the effectiveness of the method.

Upconversion Nanoparticles@Carbon Dots@Meso-SiO2 Sandwiched Core-Shell Nanohybrids with Tunable Dual-Mode Luminescence for 3D Anti-Counterfeiting Barcodes.

Development of advanced fluorescent materials for constructing a secure and unclonable encryption is urgently required; however, their application in anti-counterfeiting applications is a great challenge. In this work, we proposed and synthesized a new type of upconversion nanoparticles@carbon dots@meso-SiO2 nanohybrids by integrating two fluorescent materials of lanthanide-doped NaYF4 upconversion nanoparticles (UCNPs) and carbon dots (CDs) into mesoporous silica (mSiO2) to produce a novel sandwichlike core-shell structure and a dual-mode fluorescence from UCNPs and CDs. By tailoring the UCNP core of different upconversion luminescence, all three kinds of dual-mode luminescent UCNPs@CDs@mSiO2 nanohybrids exhibited typical RGB upconversion luminescence under a 980 nm laser and blue downconversion luminescence under a 365 nm UV light. Due to strong the hydrophilic nature of the nanohybrids, they can be further fabricated into environmentally benign luminescent inks for creating highly secured, fluorescent-based, three-dimensional anti-counterfeiting barcodes via inkjet printing. The resultant UCNPs@CDs@mSiO2 inks with a dual-mode and tunable luminescence nature endow the inkjet-printing barcodes with an extremely high encoding capacity and high security. Such dual-mode fluorescent inks and barcodes are simple to fabricate, easy to view, efficient for coding, and difficult to clone, thus making them promising nanomaterials for anti-counterfeiting applications.

Design of novel lanthanide-doped core-shell nanocrystals with dual up-conversion and down-conversion luminescence for anti-counterfeiting printing.

Development of advanced luminescent nanomaterials and technologies is of great significance for anti-counterfeiting applications in global economy, security, and human health, but has proved to be a great challenge. In this work, we design, synthesize, and characterize mono-disperse, dumbbell-shaped lanthanide-doped NaYF4@NaGdF4 core-shell nanoparticles (CSNPs) with dual-mode fluorescence by coating the NaGdF4:Ln'3+ shell onto NaYF4:Ln3+ core nanospheres via a two-step oleic acid mediated thermal decomposition process. Different from the conventional synthesis method to produce spherical nanoparticles, the epitaxial growth of the NaGdF4:Ln'3+ shell onto the nanosphere cores and the lattice mismatch between ß-NaGdF4 and ß-NaYF4 nanocrystals enable the formation of dumbbell-shaped CSNPs, as evidenced by the morphological evolution of CSNPs and as explained by the Ostwald ripening growth mechanism. By tailoring different doped lanthanide ions in the core and the shell, the resultant CSNPs exhibit tunable but different up-/down-conversion luminescence under the irradiation of a 980 nm laser and 254 nm UV light, respectively. Finally, these hydrophilic CSNPs are further fabricated into environmentally benign luminescent inks for inkjet printing to create a variety of dual-mode fluorescent patterns (peacock, temple, and a logo of "Hunan University of Technology") on different paper-based substrates (A4 paper, envelope, and postcard). Our dual-mode light-responsive CSNPs, along with an easy fabrication method, provide a simple and promising material and technique for anti-counterfeiting applications.

Synthesis of Lanthanide-Ion-Doped NaYF4 RGB Up-Conversion Nanoparticles for Anti-Counterfeiting Application.

Well-defined and mono-dispersed lanthanide-ion-doped NaYF4 up-conversion nanoparticles (UCNPs) were synthesized via thermal decomposition using lanthanide oleate as the precursor. By rational selecting the dopant pairs of the doped lanthanide ions (Y3+, Yb3+, Er3+ and Tm3+) with accurate molar ratios, three-primary-color (RGB) UCNPs which exhibited green (UCNPs-G), blue (UCNPs-B) and red (UCNPs-R) fluorescence, respectively, were prepared. The X-ray diffraction (XRD) patterns showed that the three UCNPs were purely hexagonal-phase NaYF4 crystals. Transmission electron microscopy (TEM) images revealed that the synthesized UCNPs exhibited well-defined nanosphere morphology with uniform size distribution. The average diameters were 23.95±3.35 nm for UCNPs-G, 20.63±2.59 nm for UCNPs-B, and 19.24±2.37 nm for UCNPs-R, respectively. After surface modification employing polyacrylic acid (PAA) as modifier, the obtained UCNPs were converted to be hydrophilic, which can be used as fillers to construct luminescent polymer films and luminescent ink in anti-counterfeiting application.

Hydrothermal Synthesis of PAA-Coated NaYF4:Yb3+, Er3+ Nanophosphors with Predicted Morphology, Phase and Enhanced Upconversion Luminescence Properties.

In this study, well-defined PAA-coated NaYF4:Yb3+, Er3+ nanophosphors were synthesized via a poly(acrylic acid) (PAA) mediated hydrothermal process. The rational control of initial reaction conditions, such as hydrothermal temperature, pH value of precursor-solution, added amount of PAA, and molecular weight of PAA ligand, resulted in upconversion of NaYF4:Yb3+, Er3+ phosphors with varying crystal phases (α and ß) and morphologies (e.g., nanosphere, submicrorod, microrod, microtube, and microprism). By assessing the upconversion luminescent properties of the synthesized NaYF4:Yb3+, Er3+ phosphors upon excitation by 980 nm infrared light, it was demonstrated that the ß-phase NaYF4:Yb3+, Er3+ phosphors generally presented stronger upconversion luminescent than α-phase NaYF4:Yb3+, Er3+ phosphors and orthorhombic phase of YF3:Yb3+, Er3+ sample. Additionally, the ß-phase NaYF4:Yb3+, Er3+ phosphors with hollow microtube morphology presented higher upconversion luminescent intensity than phosphors of other morphologies. This may be due to microtubes having larger surface area (inner and outer surfaces), which promoted the absorption efficiency under similar excitation conditions, therefore generating higher luminescent intensity. Findings form this study suggest for precisely controlled growth of other complex rare earth fluoride compounds and provide a reference for exploration of component-, phase- and morphology-dependent upconversion luminescence properties.

Sliding Mode Observer-Based Current Sensor Fault Reconstruction and Unknown Load Disturbance Estimation for PMSM Driven System.

This paper proposes a new scheme of reconstructing current sensor faults and estimating unknown load disturbance for a permanent magnet synchronous motor (PMSM)-driven system. First, the original PMSM system is transformed into two subsystems; the first subsystem has unknown system load disturbances, which are unrelated to sensor faults, and the second subsystem has sensor faults, but is free from unknown load disturbances. Introducing a new state variable, the augmented subsystem that has sensor faults can be transformed into having actuator faults. Second, two sliding mode observers (SMOs) are designed: the unknown load disturbance is estimated by the first SMO in the subsystem, which has unknown load disturbance, and the sensor faults can be reconstructed using the second SMO in the augmented subsystem, which has sensor faults. The gains of the proposed SMOs and their stability analysis are developed via the solution of linear matrix inequality (LMI). Finally, the effectiveness of the proposed scheme was verified by simulations and experiments. The results demonstrate that the proposed scheme can reconstruct current sensor faults and estimate unknown load disturbance for the PMSM-driven system.

Current Sensor Fault Reconstruction for PMSM Drives.

This paper deals with a current sensor fault reconstruction algorithm for the torque closed-loop drive system of an interior PMSM. First, sensor faults are equated to actuator ones by a new introduced state variable. Then, in αß coordinates, based on the motor model with active flux linkage, a current observer is constructed with a specific sliding mode equivalent control methodology to eliminate the effects of unknown disturbances, and the phase current sensor faults are reconstructed by means of an adaptive method. Finally, an αß axis current fault processing module is designed based on the reconstructed value. The feasibility and effectiveness of the proposed method are verified by simulation and experimental tests on the RT-LAB platform.

Current Sensor Fault Diagnosis Based on a Sliding Mode Observer for PMSM Driven Systems.

This paper proposes a current sensor fault detection method based on a sliding mode observer for the torque closed-loop control system of interior permanent magnet synchronous motors. First, a sliding mode observer based on the extended flux linkage is built to simplify the motor model, which effectively eliminates the phenomenon of salient poles and the dependence on the direct axis inductance parameter, and can also be used for real-time calculation of feedback torque. Then a sliding mode current observer is constructed in αß coordinates to generate the fault residuals of the phase current sensors. The method can accurately identify abrupt gain faults and slow-variation offset faults in real time in faulty sensors, and the generated residuals of the designed fault detection system are not affected by the unknown input, the structure of the observer, and the theoretical derivation and the stability proof process are concise and simple. The RT-LAB real-time simulation is used to build a simulation model of the hardware in the loop. The simulation and experimental results demonstrate the feasibility and effectiveness of the proposed method.

Online fault detection of permanent magnet demagnetization for IPMSMs by nonsingular fast terminal-sliding-mode observer.

To prevent irreversible demagnetization of a permanent magnet (PM) for interior permanent magnet synchronous motors (IPMSMs) by flux-weakening control, a robust PM flux-linkage nonsingular fast terminal-sliding-mode observer (NFTSMO) is proposed to detect demagnetization faults. First, the IPMSM mathematical model of demagnetization is presented. Second, the construction of the NFTSMO to estimate PM demagnetization faults in IPMSM is described, and a proof of observer stability is given. The fault decision criteria and fault-processing method are also presented. Finally, the proposed scheme was simulated using MATLAB/Simulink and implemented on the RT-LAB platform. A number of robustness tests have been carried out. The scheme shows good performance in spite of speed fluctuations, torque ripples and the uncertainties of stator resistance.

Complete delay-decomposing approach to asymptotic stability for neural networks with time-varying delays.

This paper is concerned with the problem of stability of neural networks with time-varying delays. A novel Lyapunov-Krasovskii functional decomposing the delays in all integral terms is proposed. By exploiting all possible information and considering independent upper bounds of the delay derivative in various delay intervals, some new generalized delay-dependent stability criteria are established, which are different from the existing ones and improve upon previous results. Numerical examples are finally given to demonstrate the effectiveness and the merits of the proposed method.