Internet usage has drastically shifted from host-centric end-to-end communication to receiver-driven content retrieval. In order to adapt to this change, a handful of innovative information/content ...centric networking (ICN) architectures have recently been proposed. One common and important feature of these architectures is to leverage built-in network caches to improve the transmission efficiency of content dissemination. Compared with traditional Web Caching and CDN Caching, ICN Cache takes on several new characteristics: cache is transparent to applications, cache is ubiquitous, and content to be cached is more ine-grained. These distinguished features pose new challenges to ICN caching technologies. This paper presents a comprehensive survey of state-of-art techniques aiming to address these issues, with particular focus on reducing cache redundancy and improving the availability of cached content. As a new research area, this paper also points out several interesting yet challenging research directions in this subject.
To further understand the effect of structural defects on the electrochemical and photocatalytic properties of TiO2, two synthetic approaches based on hydrothermal synthesis and post-synthetic ...chemical reduction to achieve oxygen defect- implantation were developed herein. These approaches led to the formation of TiO2 nanorods with uniformly distributed defects in either the bulk or on the surface, or the combination of both, in the formed TiO2 nanorods （NRs）. Both approaches utilize unique TiN nanoparticles as the reaction precursor. Electron microscopy and Brunauer-Emmett-Teller （BET） analyses indicate that all the studied samples exhibit similar morphology and similar specific surface areas. X-ray photoelectron spectroscopy （XPS） and electron paramagnetic resonance （EPR） data confirm the existence of oxygen defects （Vo）. The photocatalytic properties of TiO2 with different types of implanted Vo were evaluated based on photocatalytic H2 production. By optimizing the concentration of Vo among the TiO2 NRs subjected to different treatments, significantly higher photocatalytic activities than that of the stoichiometric TiO2 NRs was achieved. The incident photon-to-current efficiency （IPCE） data indicate that the enhanced photocatalytic activity arises mainly from defect-assisted charge separation, which implies that photo-generated electrons or holes can be captured by Vo and suppress the charge recombination process. The results show that the defective TiO2 obtained by combining the two approaches exhibits the greatest photocatalytic activity enhancement amon~ all the samples.
The fixed-frequency signal is employed in conventional high-frequency (HF) signal injection-based sensorless control schemes for interior permanent magnet synchronous motor (IPMSM) drives, which ...causes significant electromagnetic and acoustic noises. In order to diminish the additional noises, a novel pseudorandom HF (PRHF) signal injection method is investigated in this paper. Comparative analysis of the power spectra density of the induced HF currents is carried out among three different schemes: fixed-frequency HF, full-period-switch (FPS) PRHF, and half-period-switch (HPS) PRHF square-wave voltage injection. The principles and the spectral characteristics of the three PRHF injection schemes are described. Both theoretical analysis and experimental results are provided, which can agree with each other well. A theoretical basis of frequency determination is presented. Comparison of the spectral performance shows that the HPS-PRHF scheme has continuous spectra and the electromagnetic and acoustic noises can be suppressed significantly. The method is verified via a 2.2-kW IPMSM drive platform.
Photocatalytic systems capable of precisely regulating oxygen vacancy (OV) concentrations, which could help illuminate the effects of the OV concentration on N2 fixation activity, are still scarce. ...Here, we demonstrate that excessive OVs in TiO2, while increasing the adsorption activation capacity of N2 molecules, exhibit disappointing activity due to a decrease in charge separation efficiency. With optimized OV concentration, TiO2 can increase the charge separation efficiency 3-fold and show significant activation towards N2 molecules. The normalized N2 photofixation rate is 324.86 μmol h−1 g−1 (full spectrum) and the corresponding apparent quantum yield (AQY) under 365 nm illumination reaches 1.1%, which are relatively high levels compared to reports in the literature. The origin of this excellent activity is clearly attributable to the OV defect structures, which coordinate the charge separation efficiency and the dissociative adsorption capacity of N2. This work establishes the relationship between OV concentration and activity, and helps to construct a highly efficient nitrogen-fixing photocatalyst by optimizing the OV concentration.
The synthesis of dimethyl carbonate (DMC) from CO2 and methanol by Zr-doped CeO2 nanorods with different ratios of Zr/Ce has been studied at 6.8 MPa and 140 °C. The catalysts were characterized ...extensively by TEM, XRD, N2 adsorption, Raman spectroscopy, UV–vis spectroscopy, XPS, CO2-TPD, and in situ FTIR techniques. Doping of Zr atoms into the ceria lattice produced a fluorite-like solid solution, promoting the formation of oxygen vacancy sites. Zr-doped CeO2 nanorods exhibited significantly more oxygen vacancy sites than pure CeO2 nanorods. Zr0.1Ce nanorods which exhibited DMC synthesis activity also possess the highest concentration of oxygen vacancy sites. In situ FTIR studies further revealed that CO2 can adsorb on the oxygen vacancy to form bidentate carbonate and as intermediate to participate in the reaction. This study presents a strategy to design a high-efficiency CeO2-based catalysts by controlling the concentration of the surface oxygen vacancies.
To diminish the harmonic ripple in the rotor position estimation error for sensorless interior permanent magnet synchronous motor (IPMSM) drives, an adaptive linear neural (ADALINE)-network-based ...filter with a quadrature phase-locked loop (PLL) position observer is proposed. A fundamental model-based sliding-mode observer is used to obtain back electromotive force information. The harmonic content in the position estimation error caused by inverter nonlinearities and flux spatial harmonics is analyzed. According to the harmonic characteristics of the estimated rotor position, the ADALINE-network-based filter is adopted to track and compensate the selective harmonic ripple in the rotor position estimation error through continuously updating the filter weights online. Whereby, the position estimation accuracy can be improved and the position sensorless control performance can be promoted. The proposed method was verified for a 2.2-kW position sensorless IPMSM drive. Experimental results confirm the effectiveness of the method in suppressing the harmonic ripple in the rotor position estimation error.
High-frequency signal injection methods have been widely used in sensorless control of permanent-magnet synchronous motor (PMSM) drives. However, the acoustic noise and torque ripples caused by the ...injected high-frequency signal limit the application of the methods. To avoid these drawbacks, this paper proposes a position estimation method that combines derivative calculations of current and zero-voltage-vector (ZVV) injection, which is especially effective for zero- and low-speed operation of sensorless PMSM drives. This investigation mainly focuses on the extraction of rotor position from ZVV period and the improvements of the accuracy of estimated position. The PMSM equation is developed in the stationary frame when ZVV is applied. The proposed d-axis current allocation scheme ensures the application of the proposed method from no load to rated load. A modified space vector pulse width modulation (SVPWM) control strategy and a ZVV extension scheme are employed to improve the accuracy of estimated position, which also makes the method more realizable. Further, a novel current sampling method that selects two suitable phase currents for derivative calculation according to the voltage sector location is proposed, which can help reduce current derivative ripples and decrease position estimation errors. Finally, the effectiveness of the proposed position estimation strategy is verified on a 1.0-kW interior PMSM (IPMSM) drive platform.
ObjectivesUnderstanding the molecular mechanisms underlying human cartilage degeneration and regeneration is helpful for improving therapeutic strategies for treating osteoarthritis (OA). Here, we ...report the molecular programmes and lineage progression patterns controlling human OA pathogenesis using single-cell RNA sequencing (scRNA-seq).MethodsWe performed unbiased transcriptome-wide scRNA-seq analysis, computational analysis and histological assays on 1464 chondrocytes from 10 patients with OA undergoing knee arthroplasty surgery. We investigated the relationship between transcriptional programmes of the OA landscape and clinical outcome using severity index and correspondence analysis.ResultsWe identified seven molecularly defined populations of chondrocytes in the human OA cartilage, including three novel phenotypes with distinct functions. We presented gene expression profiles at different OA stages at single-cell resolution. We found a potential transition among proliferative chondrocytes, prehypertrophic chondrocytes and hypertrophic chondrocytes (HTCs) and defined a new subdivision within HTCs. We revealed novel markers for cartilage progenitor cells (CPCs) and demonstrated a relationship between CPCs and fibrocartilage chondrocytes using computational analysis. Notably, we derived predictive targets with respect to clinical outcomes and clarified the role of different cell types for the early diagnosis and treatment of OA.ConclusionsOur results provide new insights into chondrocyte taxonomy and present potential clues for effective and functional manipulation of human OA cartilage regeneration that could lead to improved health.
Polymer/inorganic particle nanocomposites (or nanodielectrics) have attracted pronounced attention for electric energy storage applications, based on a hypothesis that polymer nanodielectrics could ...combine the high permittivity of nanoparticles and the high electrical breakdown strength of the polymer matrix for enhanced dielectric performance. Although higher discharged energy densities have been reported for numerous polymer nanodielectrics, the dielectric loss mechanisms, which are extremely important for ultimate applications, are rarely discussed. In this work, we intend to address the intrinsic dielectric loss mechanisms associated with polymer nanodielectrics using a model system comprised of 70 nm BaTiO3 nanoparticles (BT NPs) in an isotactic polypropylene (PP) matrix. The effect of space charge-induced interfacial polarization on dielectric losses was investigated using bipolar and unipolar electric displacement–electric field (D-E) loop tests. Since the bipolar D-E loops always exhibited greater nonlinearity than the unipolar loops, the dielectric loss was attributed to the internal AC conduction loss from space charges (e.g., electrons) in the BT NPs, including boundary layer and bulk conductions. To mitigate the internal conduction along the PP/BT interface, atomic layer deposition of a nanolayer (5 nm) of amorphous TiO2 was applied to the BT NPs. Due to a higher resistivity, the coated amorphous TiO2 effectively reduced the boundary layer conduction loss. Nonetheless, the bulk conduction loss in BT NPs still needed to be reduced. This study suggests that more insulating high permittivity NPs are demanded for polymer nanodielectrics to enhance the dielectric performance.
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