A novel method for computing the Hilbert transform with Haar multiresolution approximation

AbstractIn this paper, an algorithm for computing the Hilbert transform based on the Haar multiresolution approximation is proposed and the L2-error is estimated. Experimental results show that it outperforms the library function ‘hilbert’ in Matlab (The MathWorks, Inc. 1994–2007). Finally it is applied to compute the instantaneous phase of signals approximately and is compared with three existing methods

Interface design for high energy density polymer nanocomposites

This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area

Heteroatom-doped core/shell carbonaceous framework materials : synthesis, characterization and electrochemical properties

Organic-inorganic hybrid core@shell nanospherical particles with 200 nm to 600 nm in diameter were formed between cyclomatrix poly(organophosphazenes) (POP) and zeolitic imidazolate framework-8 (ZIF-8) in a methanol solution at room temperature. This facile synthesis route produced core@shell spheres with controlled structure and properties, such as mono-dispersed particles, 50 nm to 100 nm shell thickness, surface area of 1557 m2 g-1 and homogenously doped Zn and heteroatoms (N, S, P, O, Cl). The POP/ZIF-8 core@shell structures were subsequently converted into porous carbonaceous materials, and investigated as anode materials in a lithium-ion coin cell battery. It showed a stable discharge capacity of 538 mA h g-1 over 250 cycles, high rate capability (0.1 C to 1 C) and excellent capacity retention, which are promising for rapid charge-discharge applications. Higher ZIF-8 loading ratio in the core@shell structure increased the capacity of the electrode material and stablised the lithiated active materials. The facile synthesis method and the carbonaceous framework materials are applicable for high performance energy storage materials in electrochemical power devices

Shape memory and self‐healing behavior of styrene–butadiene–styrene/ethylene‐methacrylic acid copolymer (SBS/EMAA) elastomers containing ionic interactions

Ionic interactions were introduced to styrene–butadiene–styrene (SBS) through blending with ethylene‐methacrylic acid copolymer (EMAA) and zinc oxide (ZnO), and a following in situ neutralization reaction between the carboxyl groups of EMAA and ZnO. The resultant SBS/EMAA (60/40 wt %) blends containing zinc carboxylate crosslinks exhibited high modulus and strong long‐time relaxation characteristics. With 74% of the carboxyl groups neutralized (zinc cation fraction of 1.7 wt %), the tensile strength of the blends was increased from 14.6 to 16.6 MPa, and the stress at 100% extension was increased from 4.8 to 8.1 MPa. The melting temperature of EMAA was utilized to trigger the shape memory behavior of SBS/EMAA, and the reversible ionic bonds endowed SBS with better shape memory and self‐healing performance. The shape‐fixing ratio and recovery ratio of SBS were increased from 90.2 and 56.5% up to 93.3 and 84.2%, respectively. When the cut surfaces of SBS/EMAA/Zn samples were brought back into contact and annealed at 100 °C for 1 h, the strength and the elongation at break were recovered by 36 and 21%, respectively. This introduction of ionic interactions through the EMAA‐ZnO neutralization reactions imparts new functions to SBS thermoplastic elastomers

Structure and electrochemical properties of hierarchically porous carbon nanomaterials derived from hybrid ZIF-8/ZIF-67 bi-MOF coated cyclomatrix poly (organophosphazene) nanospheres

Hybrid bi-ZIF nanocrystals consisting of ZIF-8/ZIF-67 were synthesised in the presence of cyclomatrix poly(organophosphazene) (POP) nanospheres and formed POP/bi-ZIF core@shell nanospheres. The POP/bi-ZIF showed excellent thermal stability up to 478°C, with well-preserved core@shell structures during carbonization at 850°C. The resultant core@shell carbon nanospheres exhibited hierarchically mesoporous structures. The porous carbon core was derived from the carbonised covalent inorganic-organic polyphosphazene framework, containing in situ doped heteroatoms such as N, P, S and O; the shell structure was derived from the bi-ZIF containing up to 40% of Zn and Co elements. The bi-ZIF derived carbon shell showed a BET surface area of 1347.76 m² g-1 and a Langmuir surface area of 1882.71 m² g-1, and the total BET surface area of the core@shell structure reached 1025.00 m² g-1. When applied as an anode material in lithium ion batteries, the core@shell carbon structure reached a charge capacity of 595 mA h g-1 with a discharge capacity of 546 mA h g-1, and remained reversible charge/discharge capacity at 400 mA h g-1 after 140 cycles, which is higher than the theoretical capacity of graphite anode. A good cycling stability with 83% capacity retention in the C-rate tests was achieved. This work provides a facile and scalable method to produce mesoporous carbon nanostructures with in situ doped metal elements and heteroatoms, which benefits the high rate electrochemical properties of lithium ion batteries

Self-healing dielectric elastomers for damage-Tolerant actuation and energy harvesting

The actuation and energy-harvesting performance of dielectric elastomers are strongly related to their intrinsic electrical and mechanical properties. For future resilient smart transducers, a fast actuation response, efficient energy-harvesting performance, and mechanical robustness are key requirements. In this work, we demonstrate that poly(styrene-butadiene-styrene) (SBS) can be converted into a self-healing dielectric elastomer with high permittivity and low dielectric loss, which can be deformed to large mechanical strains; these are key requirements for actuation and energy-harvesting applications. Using a one-step click reaction at room temperature for 20 min, methyl-3-mercaptopropionate (M3M) was grafted to SBS and reached 95.2% of grafting ratios. The resultant M3M–SBS can be deformed to a high mechanical strain of 1000%, with a relative permittivity of εr = 7.5 and a low tan δ = 0.03. When used in a dielectric actuator, it can provide 9.2% strain at an electric field of 39.5 MV m–1 and can also generate an energy density of 11 mJ g–1 from energy harvesting. After being subjected to mechanical damage, the self-healed elastomer can recover 44% of its breakdown strength during energy harvesting. This work demonstrates a facile route to produce self-healing, high permittivity, and low dielectric loss elastomers for both actuation and energy harvesting, which is applicable to a wide range of diene elastomer systems

Improved Generation of Induced Cardiomyocytes Using a Polycistronic Construct Expressing Optimal Ratio of Gata4, Mef2c and Tbx5

Direct conversion of cardiac fibroblasts (CFs) into induced cardiomyocytes (iCMs) holds great potential for regenerative medicine by offering alternative strategies for treatment of heart disease. This conversion has been achieved by forced expression of defined factors such as Gata4 (G), Mef2c (M) and Tbx5 (T). Traditionally, iCMs are generated by a cocktail of viruses expressing these individual factors. However, reprogramming efficiency is relatively low and most of the in vitro G,M,T-transduced fibroblasts do not become fully reprogrammed, making it difficult to study the reprogramming mechanisms. We recently have shown that the stoichiometry of G,M,T is crucial for efficient iCM reprogramming. An optimal stoichiometry of G,M,T with relative high level of M and low levels of G and T achieved by using our polycistronic MGT vector (hereafter referred to as MGT) significantly increased reprogramming efficiency and improved iCM quality in vitro. Here we provide a detailed description of the methodology used to generate iCMs with MGT construct from cardiac fibroblasts. Isolation of cardiac fibroblasts, generation of virus for reprogramming and evaluation of the reprogramming process are also included to provide a platform for efficient and reproducible generation of iCMs

Generation of an inducible fibroblast cell line for studying direct cardiac reprogramming: Inducible Cell Line for iCM Reprogramming

Direct reprogramming of fibroblasts into induced cardiomyocytes (iCMs) through forced expression of cardiac lineage-specific transcription factors holds promise as an alternative strategy for cardiac regeneration. To facilitate research in iCM reprogramming, we generated a suite of new tools. We developed a transformed cell line derived from mouse embryonic fibroblasts (MEF). This fibroblast cell line (MEF-T) harbors an αMHC-eGFP reporter transgene for rapid detection of newly derived iCMs. The MEF-T cell line is highly proliferative and easily transfected and transduced, making it an ideal tool for transgene expression and genetic manipulation. Additionally, we generated a Tet-On inducible polycistronic iCM reprogramming construct for the temporal regulation of reprogramming factor expression. Furthermore, we introduced this construct into MEF-T and created an inducible reprogrammable fibroblast cell line. These tools will facilitate future research in cell fate reprogramming by enabling the temporal control of reprogramming factor expression as well as high throughput screening using libraries of small molecules, non-coding RNAs and siRNAs

Bmi1 Is a Key Epigenetic Barrier to Direct Cardiac Reprogramming

Direct reprogramming of induced cardiomyocytes (iCMs) suffers from low efficiency and requires extensive epigenetic repatterning, although the underlying mechanisms are largely unknown. To address these issues, we screened for epigenetic regulators of iCM reprogramming and found that reducing levels of the polycomb complex gene Bmi1 significantly enhanced induction of beating iCMs from neonatal and adult mouse fibroblasts. The inhibitory role of Bmi1 in iCM reprogramming is mediated through direct interactions with regulatory regions of cardiogenic genes, rather than regulation of cell proliferation. Reduced Bmi1 expression corresponded with increased levels of the active histone mark H3K4me3 and reduced levels of repressive H2AK119ub at cardiogenic loci, and de-repression of cardiogenic gene expression during iCM conversion. Furthermore, Bmi1 deletion could substitute for Gata4 during iCM reprogramming. Thus, Bmi1 acts as a critical epigenetic barrier to iCM production. Bypassing this barrier simplifies iCM generation and increases yield, potentially streamlining iCM production for therapeutic purposes