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Physiologically, the intestinal barrier plays a crucial role in homeostasis and nutrient absorption and prevents pathogenic entry, harmful metabolites, and endotoxin absorption. Recent advances have highlighted the association between severely damaged intestinal barriers and diabetes, obesity, fatty liver, and cardiovascular diseases. Evidence indicates that an abated intestinal barrier leads to endotoxemia associated with systemic inflammation, insulin resistance, diabetes, and lipid accumulation, accelerating obesity and fatty liver diseases. Nonetheless, the specific mechanism of intestinal barrier damage and the effective improvement of the intestinal barrier remain to be explored. Here, we discuss the crosstalk between changes in the intestinal barrier and metabolic disease. This paper also highlights how to improve the gut barrier from the perspective of natural medicine, gut microbiota remodeling, lifestyle interventions, and bariatric surgery. Finally, potential challenges and prospects for the regulation of the gut barrier-metabolic disease axis are discussed, which may provide theoretical guidance for the treatment of metabolic diseases.

Deep neural network (DNN) is applied widely in many applications and achieves state-of-the-art performance. However, DNN lacks transparency and interpretability for users in structure. Attackers can use this feature to embed trojan horses in the DNN structure, such as inserting a backdoor into the DNN, so that DNN can learn both the normal main task and additional malicious tasks at the same time. Besides, DNN relies on data set for training. Attackers can tamper with training data to interfere with DNN training process, such as attaching a trigger on input data. Because of defects in DNN structure and data, the backdoor attack can be a serious threat to the security of DNN. The DNN attacked by backdoor performs well on benign inputs while it outputs an attacker-specified label on trigger attached inputs. Backdoor attack can be conducted in almost every stage of the machine learning pipeline. Although there are a few researches in the backdoor attack on image classification, a systematic review is still rare in this field. This paper is a comprehensive review of backdoor attacks. According to whether attackers have access to the training data, we divide various backdoor attacks into two types: poisoning-based attacks and non-poisoning-based attacks. We go through the details of each work in the timeline, discussing its contribution and deficiencies. We propose a detailed mathematical backdoor model to summary all kinds of backdoor attacks. In the end, we provide some insights about future studies.

The purpose of the present paper is to investigate the hydrogen injection strategy on the combustion performance of a natural gas/hydrogen rotary engine. Considering that apex seal leakage (ASL) is an inevitable problem in the actual working process of a rotary engine, the action of ASL cannot be ignored for an in-depth study of its combustion performance. Therefore, in this paper, a 3D dynamic simulation model that put the effect of ASL into consideration was established. Furthermore, based on the established 3D model, the combustion process of a natural gas/hydrogen rotary engine under various hydrogen injection angle (HIA) and hydrogen injection timing (HIT) was investigated. The results indicated that the hydrogen jet flow first impacted on the rotor wall after entering the cylinder, and then diffused under the action of the vortexes in the cylinder. Therefore, the HIA and HIT could change the hydrogen distribution by changing the hydrogen impact location and the intensities of the vortexes in the cylinder. In addition, the ideal hydrogen distribution at the ignition timing which could improve the combustion efficiency was given. That is, under the premise of ensuring minimized hydrogen leakage, the hydrogen should mainly distribute in the middle and the front of the cylinder, and a high hydrogen concentration is maintained near the spark plug.

Aiming at the typical optical phased array, a set of silicon-based optical phased array chip performance evaluation methods were established to provide reliable data support for the optimal design of optical phased arrays. By designing a Fourier imaging system, the optical phased array could be dynamically imaged, and simultaneous observation of near-field and far-field imaging could be achieved. On this basis, a calibration scheme was designed to optimize the initial phase of the phased array. At the same time, the characteristic parameters such as scanning speed, angle and accuracy were analyzed from theoretical derivation and simulation to the structural design of the test system.

Microfiltration is widely used in fine filtration operations, with dead-end filtration and cross-flow filtration. The microfiltration filter element or the microfiltration membrane is easy to be polluted by impurities in the water and causes fouling, resulting in flux attenuation. The flux can be expressed by Darcy’s law and attenuation model. In this paper, two industrial titanium rod sintered filter elements (?60 × 960 mm and ?60 × 960 mm) of different specifications are selected, and tap water (1.0 NTU) is used for constant pressure dead-end filtration. The amount tends to be the same, about 0.435 m3·m?2·h?1, which has nothing to do with the filtration accuracy of the filter element but only depends on the characteristics of the filter cake and the filter membrane. Through the analysis of the two models, it is found that the two filtration flux models are not universal and difficult to be applied in engineering.

Direct injection (DI) technology can improve the combustion performance of the rotary engine by realizing the fuel stratification in the cylinder. The purpose of this paper is to numerically invest...

Apex seal leakage is one of the main defects restricting the performance improvement of rotary engines. The aim of this study is to study the airflow movement in a peripheral ported rotary engine under the action of apex seal leakage. For this purpose, a three-dimensional (3D) dynamic calculation model considering apex seal leakage was first established and verified by particle image velocimetry data. Furthermore, based on the established 3D model, the flow field in the combustion chamber under the four apex seal leakage gaps (0.02, 0.04, 0.06, and 0.08 mms) and the three engine revolution speeds (2000, 3500, and 5000 RPMs) was calculated. By comparing with the flow field under the condition without leakage, the influences of the existence of apex seal leakage on the velocity field, the turbulent kinetic energy, and the volumetric efficiency in the combustion chamber were investigated. Thereinto, the influences of the existence of apex seal leakage on the velocity field is that at the intake stroke, a vortex formed in the middle of the combustion chamber under the condition without apex seal leakage, was intensified by the apex seal leakage action. At the compression stroke, irrespective of the condition with or without apex seal leakage, all vortexes in the combustion chamber are gradually broken into a unidirectional flow. However, there is an obvious “leakage flow area” at the end of combustion chamber due to the existence of apex seal leakage.

The aim of this research is to investigate the influences of apex seal leakage on the formation mechanism of flow field in a side-ported rotary engine by particle image velocimetry (PIV) and computational fluid dynamics (CFD). In this study, a PIV was used to acquire the two-dimensional (2D) flow field on the rotor housing central plane at an engine speed of 700 rpm. A three-dimensional (3D) dynamic simulation model considering leakage through apex seals was established and verified by the 2D-PIV experiment results. Thereafter, CFD analysis was used to further understand the 3D flow field in combustion chamber under the action of apex seal leakage. The simulation results showed that for the three engine speeds (2000, 3500, and 5000 rpm), in the intake stroke, the vortex generated in the front end of combustion chamber under the condition with no leakage, was strengthened and destroyed by the effects of the small (0.02 mm) and the large (0.08 mm) apex seal leakage gaps, respectively. As the apex seal leakage gap increased, the volume efficiency and the peak pressure decreased continuously. The volume efficiency and the peak pressure caused by any fixed apex seal leakage gap decreased with the increase of the engine speed. Compared with the volumetric efficiency of the condition with no leakage at 2000 and 5000 rpm, the volumetric efficiency of apex seal leakage gap of 0.08 mm decreased only by 24.6% at 5000 rpm, but by 41.2% at 2000 rpm.

This work aimed to numerically study the effect of hydrogen injection strategy on mixture formation and combustion process in a port injection (PI) rotary engine fueled with natural gas/hydrogen blends. The two main considered factors were hydrogen injection timing (IT) and hydrogen injection duration (ID). Simulation results indicated that for mixture formation, in terms of hydrogen IT, hydrogen IT of 390°CA (BTDC) is a watershed. When the hydrogen IT is before 390°CA (BTDC), the changes in hydrogen IT have little effect on the hydrogen distribution at ignition timing. Hydrogen distribution is uniform across the whole combustion chamber. However, when the hydrogen IT is after 390°CA (BTDC), with the retarded hydrogen IT, there is obvious increase in hydrogen stratification phenomenon, and more hydrogen distributes in the middle and back of combustion chamber at ignition timing. In terms of hydrogen ID, at the fixed hydrogen IT of 360°CA (BTDC), with the extended hydrogen ID, more hydrogen distributes in the back of trailing spark plug (TSP). For combustion process, to obtain a higher overall combustion rate for the PI rotary engine, the hydrogen injection strategy should make more hydrogen located at the front of TSP at ignition timing. In engineering applications, for higher peak cylinder pressure to be obtained, the continued optimization of hydrogen IT should be selected between 390°CA (BTDC) and 330°CA (BTDC). Under the hydrogen IT range of 390°CA (BTDC) to 330°CA (BTDC), the continued optimization of hydrogen ID should select between 8°CA and 24°CA.

Sentence simplification reduces semantic complexity to benefit people with language impairments. Previous simplification studies on the sentence level and word level have achieved promising results but also meet great challenges. For sentence-level studies, sentences after simplification are fluent but sometimes are not really simplified. For word-level studies, words are simplified but also have potential grammar errors due to different usages of words before and after simplification. In this paper, we propose a two-step simplification framework by combining both the word-level and the sentence-level simplifications, making use of their corresponding advantages. Based on the two-step framework, we implement a novel constrained neural generation model to simplify sentences given simplified words. The final results on Wikipedia and Simple Wikipedia aligned datasets indicate that our method yields better performance than various baselines.