Materials with an ultralow density and ultrahigh electromagnetic‐interference (EMI)‐shielding performance are highly desirable in fields of aerospace, portable electronics, and so on. Theoretical ...work predicts that 3D carbon nanotube (CNT)/graphene hybrids are one of the most promising lightweight EMI shielding materials, owing to their unique nanostructures and extraordinary electronic properties. Herein, for the first time, a lightweight, flexible, and conductive CNT–multilayered graphene edge plane (MLGEP) core–shell hybrid foam is fabricated using chemical vapor deposition. MLGEPs are seamlessly grown on the CNTs, and the hybrid foam exhibits excellent EMI shielding effectiveness which exceeds 38.4 or 47.5 dB in X‐band at 1.6 mm, while the density is merely 0.0058 or 0.0089 g cm−3, respectively, which far surpasses the best values of reported carbon‐based composite materials. The grafted MLGEPs on CNTs can obviously enhance the penetration losses of microwaves in foams, leading to a greatly improved EMI shielding performance. In addition, the CNT–MLGEP hybrids also exhibit a great potential as nano‐reinforcements for fabricating high‐strength polymer‐based composites. The results provide an alternative approach to fully explore the potentials of CNT and graphene, for developing advanced multifunctional materials.
Carbon nanotube–multilayered graphene edge plane core–shell hybrid foams are fabricated by chemical vapor deposition methods for the first time. The seamless junctions of multilayered graphene edge planes on the carbon nanotubes endow the hybrids with potential applications as high‐performance nanocomposites and ultrahigh‐performance lightweight electromagnetic‐interference shielding materials.
Display omitted
•The hierarchical microsphere CeO2 (CeO2-HS) is prepared.•The CeO2-HS is self-assembled by many ceria nanowires.•The CeO2-HS exhibits the outstanding activity toward toluene catalytic ...oxidation.•Surface oxygen vacancies control the reaction rate.
The catalytic oxidation of toluene has been investigated over pure CeO2 hierarchical catalyst for the first time. The novel CeO2 catalyst was prepared by a hydrothermal-driven assembly method. The structure of CeO2 catalyst was consisted of nanowire self-assembled hierarchical microspheres. The new hierarchical CeO2 catalyst showed much better catalytic activity than analogous nonporous catalyst by traditional hydrothermal method. The hierarchical CeO2 catalyst could reach more than 90% toluene conversion even as low as 210°C (T90) under a high space velocity of 60,000mL/(g·h). The high catalytic activities could be attributed to the large surface areas, in addition, the hierarchical porous structures provide more contents of surface oxygen vacancies for the dissociation of gaseous O2 on the surface.
As a strategy for regulating the electronic structure of metal oxides, defect engineering has been widely studied, and the concentrations and spatial distributions of metal vacancies in metal oxides ...have always resulted in unprecedented properties. Moreover, alkali metals exhibit a universal promotion effect on catalytic oxidation of formaldehyde (HCHO). Herein, a kind of birnessite-type manganese dioxide (MnO 2 ) with many Mn vacancies was hydrothermally synthesized for catalytic oxidation of HCHO. The significant effect of the K + content on the structure, morphology and catalytic activity of birnessite-type MnO 2 for HCHO oxidation was systematically studied for the first time. Initially, the increasing content of K + obviously improved the catalytic performance for HCHO oxidation due to the considerable enhancement of the lattice oxygen activity. However, due to interaction with the excess K atoms, the oxygen atoms nearest to the K atoms were more stable and their mobility decreased, which was confirmed by experimental characterization and DFT (density functional theory) calculation. Moreover, the excess K + increased the amount of surface basic sites, making CO 2 difficult to desorb. Thus, there was an optimal K + content to promote the activity of birnessite-type MnO 2 . With moderate K + content in the birnessite-type MnO 2 , excellent catalytic activity for HCHO oxidation was achieved ( T 50% = 56 °C; T 90% = 82 °C) under 100 ppm of HCHO and ∼90 L g cat −1 h −1 of gas hourly space velocity (GHSV). The present work provided an insight into the structure–activity relationship between birnessite-type MnO 2 and its catalytic activity.
•Lightweight and flexible 3D graphene microtubes membrane has been fabricated.•Interconnected edge-rich VGNs were grown on interwoven conductive CMTs networks.•The 3D GMTs membrane exhibits highly ...shows ultrahigh EMI shielding performance.
Ultralight, flexible and high-performance electromagnetic-interference (EMI) shielding performance materials are urgently required in the areas of aircraft/aerospace, portable and wearable smart electronics. Benefiting from the outstanding properties of graphene and the unique architectures, 3D assembled graphene structures have been widely applied in the field of EMI-shielding. Herein, for the first time, using Si3N4 nanowires as self-sacrificial templates with the thermal decomposition characteristics, 3D graphene microtubes (3DGMTs) membrane is fabricated by plasma enhanced chemical vapor deposition (PECVD) method, exhibiting the characteristics of free-standing and flexibility. 3DGMTs membrane assembled with silicon carbide (SiC) nanocrystals decorated edge-rich vertical graphene nanosheets (VGNs) exhibits superb EMI shielding effectiveness (SE) of around 38 dB in the frequency range of 8.2~12.4 GHz at a density of 0.0036 g cm−3 and a thickness of 1.5 mm. Considering the ultralow density and thickness, 3DGMTs membrane shows a high specific SE (SSE, defined as SE divided by mass density) of 10,556 dB cm3 g−1 in X-band, which far surpasses that of almost all the reported materials. Remarkably, our work not only provides a new idea for preparation of hollow tubular carbon materials for a wide range of applications, but also presents some fundamental insights for edge-rich VGNs applied in EMI shielding.
(1) Background: People living with type 1 diabetes (T1D) require self-management to maintain blood glucose (BG) levels in a therapeutic range through the delivery of exogenous insulin. However, due ...to the various variability, uncertainty and complex glucose dynamics, optimizing the doses of insulin delivery to minimize the risk of hyperglycemia and hypoglycemia is still an open problem. (2) Methods: In this work, we propose a novel insulin bolus advisor which uses deep reinforcement learning (DRL) and continuous glucose monitoring to optimize insulin dosing at mealtime. In particular, an actor-critic model based on deep deterministic policy gradient is designed to compute mealtime insulin doses. The proposed system architecture uses a two-step learning framework, in which a population model is first obtained and then personalized by subject-specific data. Prioritized memory replay is adopted to accelerate the training process in clinical practice. To validate the algorithm, we employ a customized version of the FDA-accepted UVA/Padova T1D simulator to perform in silico trials on 10 adult subjects and 10 adolescent subjects. (3) Results: Compared to a standard bolus calculator as the baseline, the DRL insulin bolus advisor significantly improved the average percentage time in target range (70-180 mg/dL) from 74.1%±8.4% to 80.9%±6.9% (p<0.01) and 54.9%±12.4% to 61.6%±14.1% (p<0.01) in the the adult and adolescent cohorts, respectively, while reducing hypoglycemia. (4) Conclusions: The proposed algorithm has the potential to improve mealtime bolus insulin delivery in people with T1D and is a feasible candidate for future clinical validation.
The mechanism of arsenic poisoning of CeO2–WO3 (CW) and CeO2–MoO3 (CM) catalysts during the selective catalytic reduction (SCR) of NO x with NH3 was investigated. It was found that the ratio of ...activity loss of the CW catalyst decreases as the temperature increases, while the opposite tendency was observed for the CM catalyst. The fresh and poisoned catalysts were characterized using X-ray diffraction (XRD) temperature-programmed reduction with H2 (H2-TPR), X-ray photoelectron spectra (XPS), NH3-temperature-programmed desorption (NH3-TPD), in situ DRIFTS, and in situ Raman spectroscopy. The results indicate that arsenic oxide primarily destroys the structure of the surface CeOx species in the CM catalyst but prefers to interact with WO3 in the CW catalyst. Additionally, the BET surface area, the number and stability of Lewis acid sites, and the NO x adsorption for these two types of catalysts clearly decrease after deactivation. According to the DRIFTS and Raman investigations, at low temperatures, the greater number of sites with adsorbed NH3 in the poisoned CM catalyst leads to less loss of activity than the poisoned CW catalyst. However, at high temperatures, the greater number of Lewis acid sites remaining in the poisoned CW catalyst may play an important role in maintaining the activity of this catalyst.
In this paper, a new class of orthogonal circulant matrices built from deterministic sequences is proposed for convolution-based compressed sensing (CS). In contrast to random convolution, the ...coefficients of the underlying filter are given by the discrete Fourier transform of a deterministic sequence with good autocorrelation. Both uniform recovery and non-uniform recovery of sparse signals are investigated, based on the coherence parameter of the proposed sensing matrices. Many examples of the sequences are investigated, particularly the Frank-Zadoff-Chu (FZC) sequence, the m -sequence and the Golay sequence. A salient feature of the proposed sensing matrices is that they can not only handle sparse signals in the time domain, but also those in the frequency and/or or discrete-cosine transform (DCT) domain.
•Two heat fluxes were used to evaluate the ablation of modified C/C composites.•C/C–ZrB2–ZrC–SiC has the lowest ablation rate under a heat flux of 2.38MW/m2.•Ablation rates of C/C shows the smallest ...increase with increase in heat flux.•Thermal mismatch and evaporation of SiO2 dominate variations in the ablation behavior.
Carbon/carbon composites modified by ZrB2–ZrC–SiC particles (C/C–Z–SiC), C/C–Z and C/C were ablated by oxyacetylene torch using two different heat fluxes to investigate the effect of doped ceramic particles. Results indicated that C/C–Z–SiC had the best ablation property in heat flux of 2.38MW/m2 whereas their ablation rates increased fastest when heat flux rising from 2.38 to 4.18MW/m2. C/C composites had the poorest ablation property in the lower heat flux and their ablation rates increased slowest. Thermal mismatch of Z, SiC and C and evaporation of SiO2 induced the various ablation behavior.
A new iterative image reconstruction algorithm for electrical capacitance tomography (ECT) is proposed which is based on iterative soft thresholding of a total variation penalty and adaptive ...reweighted compressive sensing. This algorithm encourages sharp changes in the ECT image and overcomes the disadvantage of the l 1 minimization by equipping the total variation with an adaptive weighting depending on the reconstructed image. Moreover, the non-linear effect is also partially reduced due to the adoption of an updated sensitivity matrix. Simulation results show that the proposed algorithm recovers ECT images more precisely than existing state-of-the-art algorithms and therefore is suitable for the imaging of multiphase systems in industrial or medical applications. Specifically, quantitative permittivity measurements can be recovered.
Secondary problems, such as the occurrence of side reactions and the accumulation of by-products, are a major challenge in the application of wet denitrification technology through urea solution. We ...revealed the formation mechanism of urea nitrate and clarified the main and side reaction paths and key intermediates of denitrification. Urea nitrate would be separated from urea absorption solution only when the concentration product of urea, H+ and NO3− was greater than 0.87~1.22 mol3/L3. The effects of the urea concentration (5–20%) and reaction temperature (30–70 °C) on the denitrification efficiency could be ignored. Improving the oxidation degree of the flue gas promoted the removal of nitrogen oxides. The alkaline condition was beneficial to the dissolution process, while the acidic condition was beneficial to the reaction process. As a whole, the alkaline condition was the preferred process parameter. The research results could guide the optimization of process conditions in theory, improve the operation efficiency of the denitrification reactor and avoid the occurrence of side reactions.
PDF
