Lithium–sulfur (Li–S) batteries have a distinct advantage over other rechargeable battery systems since their high specific energy and low cost. However, the diffusion of polysulfides from cathode to ...anode leads to poor electrochemical stability of Li–S batteries, which is a main factor that restricts their further development. Herein, for the first time we present a separator with nitrogen-doped porous hollow carbon sphere (NHC) coating, with which Li–S cells enormously improve the utilization of active material and enhance excellent electrochemical performance. An initial discharge capacity of 1656 mAh g−1 (0.2 C) and a low fading rate of 0.11% per cycle within 500 cycles (1 C) are achieved, which ascribe to the chemical and physical adsorption properties of porous and nitrogen-doped NHCs. The NHC-decorated separator is of low cost and can effectively improve energy density of Li–S cells, exhibiting potential for further development of Li–S batteries.
Nitrogen-doped porous hollow carbon spheres are prepared by pyrolysis of a polydopamine (PDA) carbon precursor on the surface of silicon dioxide (SiO2) temple. After washed with HF, the NHCs are coated onto one side of the separator with a slurry-coated method. With the NHC-decorated separator, an initial discharge capacity of 1656 mAh g−1 (0.2 C) and a low fading rate of 0.11% per cycle within 500 cycles (1 C) are achieved. The excellent results are attributed to the high specific surface area and pore volume of the NHCs which ensure electrolyte infiltration and act as a barrier for polysulfides. Furthermore, the high nitrogen content in NHCs can improve electronic conductivity and enhance interaction between nitrogen atoms and polysulfides. Display omitted
•NHCs are prepared by pyrolysis of a PDA carbon precursor.•NHC-decorated separator exhibits excellent electrochemical performance.•NHC-decorated separator would be a promising solution for Li–S batteries.
Multi-walled carbon nanotube/selenium composites (MWCNT/Se) are prepared via a simple solution-based processing strategy using ethylenediamine as the solvent. The selenium nanoparticles in diameter ...of about 100 nm are homogeneously deposited on the network of multi-walled carbon nanotubes in the composites. Compared with multi-walled carbon nanotube/selenium composites by melt-infusing method (MWCNT/Se-M), the multi-walled carbon nanotube/selenium composites by solution-based process (MWCNT/Se–S) can deliver a much higher initial discharge capacity (645.7 mAh g−1) and a better cycling stability (355.5 mAh g−1 remaining at a rate of 0.5C after 100 cycles). Even at 4C, it still exhibits a reversible capacity of 468.7 mAh g−1. The superior electrochemical properties of multi-walled carbon nanotube/selenium composites via solution-based process could be ascribed to the diminished size of selenium and uniform distribution of selenium nanoparticles in carbon matrix.
•Se/MWCNT composites were prepared by a solution-based method for Li–Se batteries cathode.•The solution method leads to a reduced particle size and homogenous distribution of Se in MWCNT network.•Se/MWCNT composites prepared by solution process exhibit good cycling and rate performance.•This method may provide a rational direction to design C/Se nanocomposites.
As an attractive metal‐free conjugated polymer, graphitic carbon nitride (g‐C3N4) has attracted extensive attention in the field of solar energy conversion and storage as a visible light responsive ...hydrogen evolution. However, the photocatalytic efficiency of g‐C3N4 still has great room for improvement. Herein, a highly efficient visible‐light‐driven okra‐like tubular g‐C3N4photocatalyst (TCNMCA‐PImM) was synthesized via pyrolysis of a poly‐(imidazolium‐methylene) chloride (PImM)‐mediated molecular assembly prepared by a hydrothermal process of a solution containing PImM, melamine, and KOH, in which PImM acts as an electronic structure regulator owing to its strong hydrogen bond, π‐π interaction, and van der Waals force. On the basis of maintaining tri‐s‐triazine structure, the increase of graphitic N promotes the separation and transfer efficiency of photogenerated electrons and holes through the electron structure adjustment. The photocatalyst displays the notably promoted photocatalytic performance for H2 generation under visible‐light illumination. The optimized photocatalyst shows 1902 μmol h−1 g−1 of hydrogen evolution rate, which is 25.7 times higher than that of bulk g‐C3N4. The developed polymeric carbon nitride with unique geometric structure and electronic properties can be extended to other applications like CO2 capture for carbon neutralization strategy.
Solar Hydrogen Production: An efficient visible‐light‐driven okra‐like tubular g‐C3N4 photocatalyst for solar hydorgen was developed via a poly‐(imidazolium‐methylene) chloride (PImM)‐mediated assembly strategy, in which PImM acts as an electronic structure regulator.
A polydimethylsiloxane (PDMS)-based stretchable metadevice for dual-band switching of terahertz radiation is experimentally demonstrated. The metasurface can efficiently excite dipole resonance of ...the metal structure and the surface Bloch mode generated by the periodic lattice substrate. In the tensile deformation operation, these two resonant modes show significant frequency shift sensitivity characteristics, which provides a feasible solution for the realization of dual-band terahertz switches. A transmittance modulation depth of 90% is achieved by the dipole resonance, with a frequency shift of 0.14 THz. The other transmittance modulation depth of 65% is achieved by the surface Bloch mode, with a frequency shift of 0.4 THz. The broad tuning of 0.4 THz is attributed to the surface mode is period-sensitive. This approach provides a promising method for broad frequency tuning of stretchable metasurfaces.
The main difficulty of full waveform inversion (FWI) based on local optimization methods is that it tends to trap in local minima or cycle-skipping associated with inaccurate initial models and ...waveform misfit functions, especially for elastic media. To address this issue, we first discuss the relationship between reverse time migration (RTM) and traditional reflection FWI (RFWI). Then, we present an elastic RFWI (ERFWI) methodology. However, for ERFWI, high nonlinearity still exists in data residuals related misfit function, when true amplitude migration is not adopted. To further mitigate the cycle skipping and avoid the requirements of true amplitude migration, we develop a traveltime-based ERFWI method to update the low-wavenumber components of P- and S-velocity models. The traveltime-based ERFWI only eliminates traveltime residuals along the wave-path of sensitivity kernels to extract the long-wavelength background of the middle and deep parts. Once the traveltime of reflected waves is described correctly, the inversion result using the traveltime-based ERFWI method could be used as a velocity model for prestack depth migration (PSDM) or as an initial model for the conventional FWI to obtain high-resolution velocity model. The final results by combining traveltime-based ERFWI and conventional FWI illustrate that the combined method can obtain an improved result, compared with regular FWI methods.
•Comparing the characteristics of RTM and RFWI to explain the advantage of RFWI•Proposing the ERFWI methodology•Giving the generalized gradient based on weighted cross-correlation objective function•Improving the feasibility of ERFWI using the traveltime gradient operator
Full-waveform inversion (FWI) is a successful technique that attempts to build high-resolution velocity models by minimizing the residuals between observed and calculated data after a series of ...iterations. However, its successful application still relies on the quality of the estimated initial velocity model, as well as on the design of a suitable hierarchical workflow. If the initial model is far away from the true model, the widely used gradient-based FWI will inevitably get trapped into meaningless local minima. Given that the properties of the low-wavenumber components can help construct the initial model and overcome cycle skipping, we propose a low-wavenumber update FWI method based on the Hilbert transform called the hybrid method. This method provides a new form of FWI in the time-space domain that appears to be capable of enhancing the low-wavenumber updates. In this method, the updates of low wavenumbers and high wavenumbers are divided into two parts. In the first step, a gradient formula based on the Hilbert transform plays a key role in updating the low-wavenumber components. The gradient is formed by cross-correlation of upgoing and downgoing waves of source and residual wavefields. Instead of using the wavefield decomposition method in the frequency-wavenumber domain with high computational complexity, we apply a novel method to extract the upgoing and downgoing wavefields in the time-space domain. In addition to the acceptable computational burden, the memory is reduced greatly. The second step is the standard FWI, and its task is to update the high-wavenumber components. Numerical tests on an anomaly model and the Marmousi model demonstrate the effectiveness of the hybrid method for extracting low-wavenumber components even for noisy data or when low-frequency data are missing.
•Constructing an improved wavefield decomposition method in time-space domain using Hilbert transform•Proposing the low-wavenumber updates method of FWI based on the improved wavefield decomposition method•Synthetic data with noise or low-frequency missing are adopted to demonstrate the performance of the proposed method.
Accurate initial model or available low-frequency data is an important factor in the success of full waveform inversion (FWI). The low-frequency helps determine the kinematical relevant components, ...low-wavenumber of the velocity model, which are in turn needed to avoid FWI trap in local minima or cycle-skipping. However, in the field, acquiring data that <5 Hz is a challenging and expensive task. We attempt to find the common point of low- and high-frequency signal, then utilize the high-frequency data to obtain the low-wavenumber velocity model. It is well known that the instantaneous amplitude envelope of a wavelet is invariant under frequency shift. This means that resolution is constant for a given frequency bandwidth, and independent of the actual values of the frequencies. Based on this property, we develop a frequency shift filter (FSF) to build the relationship between low- and high-frequency information with a constant frequency bandwidth. After that, we can use the high-frequency information to get a plausible recovery of the low-wavenumber velocity model. Numerical results using synthetic data from the Marmousi and layer model demonstrate that our proposed envelope misfit function based on the frequency shift filter can build an initial model with more accurate long-wavelength components, when low-frequency signals are absent in recorded data.
•Proving the reliability of low-frequency information recovered by envelope inversion•Proposing the FSF based on the invariance of wavelet envelope under frequency shift•Building a relationship between low- and high-frequency signals with constant frequency bandwidth•Synthetic data is adopted to demonstrate the performance of the proposed FSF method.
IntroductionLong-term cognitive impairment is one of the most common complications of critical illness among survivors who receive mechanical ventilation. Recommended oxygen targets during mechanical ...ventilation vary among international guidelines. Different oxygen targets during mechanical ventilation have the potential to alter long-term cognitive function due to cerebral hypoxemia or hyperoxemia. Whether higher, intermediate or lower SpO2 targets are associated with better cognitive function at 12-month follow-up is unknown.Methods and analysisThe Pragmatic Investigation of optimaL Oxygen Targets (PILOT) trial is an ongoing pragmatic, cluster-randomised, cluster-crossover trial comparing the effect of a higher SpO2 target (target 98%, goal range 96%–100%), an intermediate SpO2 target (target 94%, goal range 92%–96%) and a lower SpO2 target (target 90%, goal range 88%–92%) on clinical outcomes in mechanically ventilated patients admitted to the medical intensive care unit at a single centre in the USA. For this ancillary study of long-term Cognitive Outcomes (CO-PILOT), survivors of critical illness who are in the PILOT trial and who do not meet exclusion criteria for CO-PILOT are approached for consent. The anticipated number of patients for whom assessment of long-term cognition will be performed in CO-PILOT is 612 patients over 36 months of enrolment. Cognitive, functional and quality of life assessments are assessed via telephone interview at approximately 12 months after enrolment in PILOT. The primary outcome of CO-PILOT is the telephone version of the Montreal Cognitive Assessment. A subset of patients will also complete a comprehensive neuropsychological telephone battery to better characterise the cognitive domains affected.Ethics and disseminationThe CO-PILOT ancillary study was approved by the Vanderbilt Institutional Review Board. The results will be submitted for publication in a peer-reviewed journal and presented at one or more scientific conferences.
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