Liquid crystal elastomers (LCEs) have recently shown great potential in the applications of soft robotics, biomedical devices, active morphing structures, self-regulating systems and biomimetic ...demonstrations. Physical properties of LCEs highly depend on their crosslinking and the alignment of mesogens in the polymer network. Different strategies have been adopted to control and program the alignment of mesogens in LCEs over the recent decades, including stretching a loosely crosslinked LCE during its second-step crosslinking reaction, application of a strong magnetic or electrical field onto an LCE during its crosslinking process, and crosslinking a LCE thin film on the top of a surface with predesigned molecular texture. In the most recent decade, dynamic covalent bonds, which can undergo exchange reactions with or without external stimuli, have been introduced into LCEs to enable facile programing of mesogen orientation in the elastomer. In addition to the programmability, the LCEs with dynamic covalent bonds have also shown great recyclability, self-healing abilities and reprogrammability. In this article, we will review the recent progress in the synthesis, programming and application of LCEs with dynamic covalent bonds. We will also discuss the challenges and research opportunities in the field.
A rhodamine‐based molecule, Rh‐OH, is synthesized. Rh‐OH exhibits a reversible mechanochromic luminescent character but a passivating response to UV light. An elastomeric polymer film based on ...polyurethane with embedded Rh‐OH is prepared via a polycondensation reaction. The film shows mechanochromic and photochromic properties with reversible color change, which originates from the isomerization of the Rh‐OH molecule from a twisted spirolactam in the ring‐closed form to a planarized zwitterionic structure in the ring‐open state.
Mechanofluorochromic or piezochromic fluorescence chemistry involves the switching and tuning of the luminescent properties of solid‐state materials induced by exogenous forces, such as grinding, ...shearing, compression, tension, and so forth. Up until now, most reported mechanochromic systems, including liquid crystals, organic molecules, organometallic compounds, polymers, and dye‐doped polymers, have displayed reversible two‐color changes, which arise from either supramolecular or chemical structure transformations. However, fluorescent materials that undergo mechanically induced multicolor changes remain rare; this Minireview is focused on such materials. Topics are categorized according to the different applied forces that are required to induce the multicolor change, including mechanical control of either the supramolecular structures or the chemical structures, and mechanical control of both the supramolecular structures and chemical structures.
Karma Chameleon: This Minireview focuses on the mechanisms and strategies for constructing fluorescent materials that undergo mechanically induced multicolor changes. The topics are categorized according to the different applied forces that are required to induce the color change, including mechanical control of either the supramolecular structures or the chemical structures, and mechanical control of both the supramolecular structures and chemical structures.
Automatic classification of tissue types of region of interest (ROI) plays an important role in computer-aided diagnosis. In the current study, we focus on the classification of three types of brain ...tumors (i.e., meningioma, glioma, and pituitary tumor) in T1-weighted contrast-enhanced MRI (CE-MRI) images. Spatial pyramid matching (SPM), which splits the image into increasingly fine rectangular subregions and computes histograms of local features from each subregion, exhibits excellent results for natural scene classification. However, this approach is not applicable for brain tumors, because of the great variations in tumor shape and size. In this paper, we propose a method to enhance the classification performance. First, the augmented tumor region via image dilation is used as the ROI instead of the original tumor region because tumor surrounding tissues can also offer important clues for tumor types. Second, the augmented tumor region is split into increasingly fine ring-form subregions. We evaluate the efficacy of the proposed method on a large dataset with three feature extraction methods, namely, intensity histogram, gray level co-occurrence matrix (GLCM), and bag-of-words (BoW) model. Compared with using tumor region as ROI, using augmented tumor region as ROI improves the accuracies to 82.31% from 71.39%, 84.75% from 78.18%, and 88.19% from 83.54% for intensity histogram, GLCM, and BoW model, respectively. In addition to region augmentation, ring-form partition can further improve the accuracies up to 87.54%, 89.72%, and 91.28%. These experimental results demonstrate that the proposed method is feasible and effective for the classification of brain tumors in T1-weighted CE-MRI.
Optically driven active materials have received much attention because their deformation and motion can be controlled remotely, instantly, and precisely in a contactless way. In this study, we ...investigated an optically actuated elastomer with rapid response: polydopamine (PDA)-coated liquid crystal elastomer (LCE). Because of the photothermal effect of PDA coating and thermal responsiveness of LCE, the elastomer film contracted significantly with near-infrared (NIR) irradiation. With a fixed strain, light-induced actuating stress in the film could be as large as 1.5 MPa, significantly higher than the maximum stress generated by most mammalian skeletal muscle (0.35 MPa). The PDA-coated LCE films could also bend or roll up by surface scanning of an NIR laser. The response time of the film to light exposure could be as short as 1/10 of a second, comparable to or even faster than that of mammalian skeletal muscle. Using the PDA-coated LCE film, we designed and fabricated a prototype of robotic swimmer that was able to swim near the water–air interface by performing “swimming strokes” through reversible bending and unbending motions induced and controlled by an NIR laser. The results presented in this study clearly demonstrated that PDA-coated LCE is a promising optically driven artificial muscle, which may have great potential for applications of soft robotics and optomechanical coupling devices.
Asserting its independence: A single organic molecule containing pyrene and rhodamine B chromophores separated by a peptide spacer (see structure) formed a mechanochromic material whose fluorescence ...could be switched from blue to bluish‐green and reddish by grinding. Modulation of the overlapped packing pattern of the pyrene excimer for blue emission was crucial for the reversible tricolored switching observed.
Variational Mode Decomposition (VMD) can decompose signals into multiple intrinsic mode functions (IMFs). In recent years, VMD has been widely used in fault diagnosis. However, it requires a preset ...number of decomposition layers
and is sensitive to background noise. Therefore, in order to determine
adaptively, Permutation Entroy Optimization (PEO) is proposed in this paper. This algorithm can adaptively determine the optimal number of decomposition layers
according to the characteristics of the signal to be decomposed. At the same time, in order to solve the sensitivity of VMD to noise, this paper proposes a Modified VMD (MVMD) based on the idea of Noise Aided Data Analysis (NADA). The algorithm first adds the positive and negative white noise to the original signal, and then uses the VMD to decompose it. After repeated cycles, the noise in the original signal will be offset to each other. Then each layer of IMF is integrated with each layer, and the signal is reconstructed according to the results of the integrated mean. MVMD is used for the final decomposition of the reconstructed signal. The algorithm is used to deal with the simulation signals and measured signals of gearbox with multiple fault characteristics. Compared with the decomposition results of EEMD and VMD, it shows that the algorithm can not only improve the signal to noise ratio (SNR) of the signal effectively, but can also extract the multiple fault features of the gear box in the strong noise environment. The effectiveness of this method is verified.
There has been an intensive international effort to develop high-order Computational Fluid Dynamics （CFD） methods into de- sign tools in aerospace engineering during the last one and half decades. ...These methods offer the potential to significantly im- prove solution accuracy and efficiency for vortex dominated turbulent flows. Enough progresses have been made in algorithm development, mesh generation and parallel computing that these methods are on the verge of being applied in a production design environment. Since many review papers have been written on the subject, I decide to offer a personal perspective on the state-of-the-art in high-order CFD methods and the challenges that must be overcome.
In photocatalytic systems, the transfer of electrons from semiconductor nanostructures to the reduction cocatalysts is the key electronic process, which determines the effective separation of ...photogenerated charge carriers, and is sensitively influenced by the band structures of the contacts. Due to improper adoption of cocatalysts, interfacial charge transfer is usually suffering from excessive energy dissipation by thermionic emission, which kinetically prevents this electronic process and eventually aggravates the recombination of photogenerated charge carriers. Unfortunately, this issue has hardly been consciously considered. The formed potential barriers, which are mainly determined by the adoption of cocatalyst, kinetically predominates the interfacial charge transfer as well as the whole photocatalytic reaction. In this work, inspired by theoretical simulation, we adopt platinum and MoS2 that deposited on semiconductor nanostructures as the models to demonstrate the energy dissipation that kinetically influences the interfacial charge transfer. Despite high catalytic activity, the intolerably high energy dissipation for interfacial charge transfer hides the superiority of platinum, resulting in an inferior photocatalytic performance to that of MoS2. Our work rationally unfastens the deliberative consideration of intrinsic activity and prompts the exploration of cocatalysts for photocatalyst designing.
Efficient and rapid detection of pathogens plays an important role in food safety, disease prevention, diagnosis and environmental monitoring. The traditional method for pathogen detection is plate ...culturing, consuming lots of time on separating, culturing and identifying pathogens by morphological characteristics, biochemical and serological reactions. It is a great advantage to take nucleic acids of pathogens as targets for detection because of higher specificity. The polymerase chain reaction (PCR) greatly shortens the time of pathogen detection but it is heavily dependent on temperature control instruments. Although isothermal amplification overcomes the defects of temperature control, it requires multiple enzymes or complex primers. Here, we summarize the recent advances in the amplification free methods for pathogen detection which are well developed for their simplicity, sensitivity and rapidity. Without nucleic acid amplification, we can directly detect the original nucleic acids of the samples rather than amplified nucleic acids. The amplification free methods for nucleic acid detection are mainly classified into electrochemical biosensors, optical biosensors and piezoelectric plate biosensors. This article describes the principles and compares the advantages and disadvantages of these methods. We further discuss the challenges and directions of this field, providing an overview for future researchers.
•Nucleic acid detection of pathogens is important in food safety, agricultural production and medical diagnosis.•We comprehensively review recent advances in pathogen detection without nucleic acid amplification.•We focus on the advantages and disadvantages of electrochemical, optical and piezoelectric plate detection.•The trends of well-developed nanotechnology and microfluidics promoting amplification free detection are discussed.
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