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Introduction: Acute appendicitis is a common surgical emergency. This study aims to determine whether there are any delays in patients attending the emergency department, potentially leading to an increase in the rates of complicated appendicitis and post-operative complications during the fifth wave of the coronavirus disease 2019 (COVID-19) pandemic in a local cluster in Hong Kong. Methods: In this retrospective cohort study, we analysed 138 patients diagnosed with acute appendicitis during the fifth wave of the COVID-19 pandemic and pre-COVID-19 period. The main study parameters were the duration between the onset of symptoms and attendance to the accident and emergency department, severity of appendicitis, post-operative complication(s), operation time and total hospital length of stay. Results: There was no delay in presentation between the two groups of patients. The rates of complicated appendicitis and post-operative complications were comparable between the two groups. There was a significantly shorter length of stay for patients with acute appendicitis patients during the fifth wave of the pandemic. Conclusion: The perspective of the general public towards the COVID-19 pandemic is changing. Increased understanding of the COVID-19 infection and availability of antiviral medications against COVID-19 could be useful to eliminate patient's anxiety when attending medical care in public hospitals. [ABSTRACT FROM AUTHOR]

Fe2Si nanoparticles attached single-walled carbon nanotubes (Fe2Si-SWCNTs) have been mass produced by a direct current arc discharge in H2/Ar. The Fe2Si-SWCNTs nanocomposites with different Si-Fe ingredient atomic ratios have a network nanostructure and provide good electrical conductivity and impedance matching. The relative complex permittivity and permeability can be adjusted by synergetic interactions between Fe2Si nanoparticles and SWCNTs in the frequency range of 2–18 GHz. The reflection loss of Fe2Si-SWCNTs nanocomposites reaches −49.9 dB at 8.08 GHz when the filler loading is only 20 wt. % in paraffin, and the effective absorption bandwidth is up to 4.32 GHz (5.92–10.24 GHz) corresponding to a thickness of 3.4 mm. This work not only paves the way for practical application of SWCNTs but also provides a kind of efficient electromagnetic wave absorber. [ABSTRACT FROM AUTHOR]

The electromagnetism and microwave absorption properties were investigated in the frequency range of 2–18 GHz for the nanocomposites NiCo-SWCNTs/CoFe2O4consisting of Ni-Co attached single-walled carbon nanotubes (NiCo-SWCNTs) and CoFe2O4 nanocrystals with different ingredient weight ratios. NiCo-SWCNTs were mass-produced by a direct current arc discharge in helium and CoFe2O4 was synthesized by a sol-gel method. Premium microwave absorption properties (mainly in Ku-band, i.e., 12–18 GHz) were obtained due to the appropriate combination of the complex permeability and permittivity resulting from the magnetic nanocrystals and high-crystalline NiCo-SWCNTs. The NiCo-SWCNTs/CoFe2O4nanocomposites with 15 wt.% NiCo-SWCNTs exhibited the best microwave absorption property, whose reflection loss (RL) value reached -47.9 dB at 14.7 GHz and the absorption bandwidth (RL < -10 dB) was up to 7.1 GHz (from 10.5 to 17.6 GHz) with a matching thickness of only 1.8 mm. Our results indicate that the studied nanocomposite could be used as a promising candidate for lightweight microwave absorption materials. [ABSTRACT FROM AUTHOR]

Background: Continued or recurrent bleeding after endoscopic treatment for bleeding ulcer is o major adverse prognostic factor. Identification of such ulcers may allow for alternate treatments. Aim: To determine factors [...]

The nanocomposites, consisting of BaFe12O19 ferrite and few-layer graphene sheets (FL-GSs) in various weight ratios (1--9 wt. %), were fabricated by a mechanical mixing method. The high-crystalline FL-GSs were prepared by direct current arc discharge evaporation of pure graphite electrodes in an H2-Ar gas mixture. We measured the electromagnetic properties, including effective magnetic permeability and effective permittivity in addition to microwave absorption performance, of the FL-GSs/BaFe12O19 nanocomposites compared with the pristine BaFe12O19 nanoparticles (NPs). The nanocomposite FL-GSs/BaFe12O19 with the optimal performance (6 wt. % FL-GSs) exhibited an effective microwave absorption (<-10 dB) bandwidth of 5.8 GHz with a thickness of 2.2 mm, 53% higher than that of the pristine BaFe12O19 NPs. Meanwhile, this nanocomposite had the minimum reflection loss of -49.7 dB at 8.4 GHz with a thickness of 2.8 mm, three times greater than those without FL-GSs. These performances result from a simultaneous increase in both magnetic and dielectric losses possibly due to synergistic effects of BaFe12O19 and FL-GSs. In such nanocomposites, both magnetic loss from BaFe12O19 and dielectric loss from FL-GSs contribute to the absorbing performances. Adding FL-GSs as dielectric fillers enhances the impedance matching of the nanocomposites compared with the pristine BaFe12O19 NPs based on the magnetic loss alone. Our results indicate that the incorporation of high-crystalline nanocarbon materials into ferrite oxides can provide high microwave absorption intensity and broad effective absorption bandwidth, while maintaining high thermal stability. [ABSTRACT FROM AUTHOR]

The active control of internal transport barriers (ITBs) is an important issue to achieve high performance plasma in a fusion reactor. A critical challenge of ITB control is to increase the ITB position. The ITBs with internal kink modes (IKMs), such as fishbone (FB) instability and long-live mode (LLM) with mode number of m / n = 1/1 are frequently observed on HL-2A tokamak in neutral beam heated discharges. The correlation of FB instability/LLM with ITBs is analyzed in order to extend the ITB radius. It has been revealed that FB instability and LLM are often excited after the ITB formation. Therefore, FB instability and LLM play no role in triggering ITBs on HL-2A tokamak. On the other hand, they may slow down the outward radial expansion and then shrink the foot position of ITB, and damp the gradient growth of ion temperature and rotation velocity. Since the perturbation of LLM is weaker than that of FB instability, the shrinking effect of ITB foot and braking effect on gradient growth are slighter than those of FB instability. Compared with the LLM, FB instability routinely appears in plasmas with lower density, higher heating power and lower plasma current. In addition, large ITBs without IKMs are also discussed on HL-2A tokamak. The large ITB is the largest one, the FB ITB is the strongest one and the LLM ITB is the widest one in three ITBs, where the ‘large’, ‘strong’ and ‘wide’ qualifications correspond to ITB position ρ ITB, the normalized temperature gradient R /LT, and its width W / a. Therefore, the large ITB position may be obtained if the IKMs are effectively controlled in a tokamak. [ABSTRACT FROM AUTHOR]

Using machine learning (ML) techniques to develop disruption predictors is an effective way to avoid or mitigate the disruption in a large-scale tokamak. The recent ML-based disruption predictors have made great progress regarding accuracy, but most of them have not achieved acceptable cross-machine performance. Before we develop a cross-machine predictor, it is very important to investigate the method of developing a cross-tokamak ML-based disruption prediction model. To ascertain the elements which impact the model's performance and achieve a deep understanding of the predictor, multiple models are trained using data from two different tokamaks, J-TEXT and HL-2A, based on an implementation of the gradient-boosted decision trees algorithm called LightGBM, which can provide detailed information about the model and input features. The predictor models are not only built and tested for performance, but also analyzed from a feature importance perspective as well as for model performance variation. The relative feature importance ranking of two tokamaks is caused by differences in disruption types between different tokamaks. The result of two models with seven inputs showed that common diagnostics is very important in building a cross-machine predictor. This provided a strategy for selecting diagnostics and shots data for developing cross-machine predictors. [ABSTRACT FROM AUTHOR]

The effects of a coherent mode (CM) at a frequency of f = 13–16 kHz on the redistribution of divertor particle flux have been studied in HL-2A H-mode plasmas using multiple diagnostics. The experimental results demonstrate that a CM localized at the middle of the pedestal results in outward particle transport, limiting the growth of the pedestal density gradient in the recovery phase of the pedestal, leading to a substantial increase in the localized particle flux striking the outer divertor target, which clearly deviates from the primary peak at the strike point. These observations indicate that the CM might play a crucial role in redistributing the divertor particle flux, which is important for understanding and controlling the divertor heat flux in future fusion-relevant devices. [ABSTRACT FROM AUTHOR]

The electromagnetism and microwave absorption properties of SmCo coated single-wall carbon nanotubes (SmCo@SWCNTs) and Ni0.5Zn0.5Fe2O4 ferrite (NiZn-ferrite) nanocrystalline composites with different ingredient weight ratios were investigated in the frequency range of 2-18 GHz. SmCo@SWCNTs were prepared by a direct current arc discharge method. NiZn-ferrite nanocrystalline was synthesized by a sol-gel method. The electromagnetic properties of the nanocomposites in the paraffin matrix were measured by a vector network analyzer. The Debye equation and Bruggeman symmetric medium equation were introduced to explain the dielectric properties of the nanocomposites, and the mechanisms for the dielectric and magnetic losses were discussed. The experiment results reveal that the absorbing properties of the nanocomposites could be improved by tuning for a suitable weight ratio between SmCo@SWCNTs and NiZn-ferrite nanocrystallines. The reflection loss simulation calculations demonstrated that the nanocomposite could be excellent materials for microwave absorption. [ABSTRACT FROM AUTHOR]

We have successfully developed a C60:LiF/BCP (bathocuproine) bilayer-buffer structure to optimize both the light absorption enhancement and the exciton-blocking at the cathode interface of a small molecular photovoltaic cell based on the archetypical CuPc/C60 structure. The function of the C60:LiF layer is to serve as an optical spacer and is found to yield a peak power conversion efficiency (PCE) with a 50 wt. % LiF at a thickness of 30 nm. A BCP layer is added between the optimized C60:LiF layer and the Al metal electrode to function as a barrier for excitons. This combined bilayer-buffer structure yields an optimal performance in short circuit current (Jsc) and PCE. A detailed study using a single carrier electron-only structure and a numerical simulation of optical electric-field distribution suggests that C60:LiF layer enhances light absorption at long wavelengths. [ABSTRACT FROM AUTHOR]