Search

To address the issue of reduced positioning and anti-swing accuracy of bridge cranes under disturbed conditions within a prescribed time, a positioning and anti-swing control algorithm, based on a prescribed-time disturbance observer, is proposed. Unlike existing research, the novel disturbance observer is designed to accurately estimate disturbances within a prescribed time, ensuring precise disturbance compensation. This allows for high-precision positioning and anti-swing of bridge cranes under disturbed conditions within a prescribed time. Firstly, a prescribed-time disturbance observer is designed to ensure accurate disturbance estimation. Secondly, a new prescribed-time sliding mode surface and a prescribed-time reaching law with a recursive structure are designed to ensure that the system state converges accurately within the prescribed time. Finally, theoretical analysis and simulation verify that the proposed control algorithm achieves the control objective of high-precision positioning and anti-swing of bridge cranes under disturbed conditions within a prescribed time. [ABSTRACT FROM AUTHOR]

The divergent synthesis of dihydropyrimidouracil and pyrimidouracil derivatives from N‐uracil amidines and tertiaryamines by an oxidative C(sp3)−N cleavage cascade cyclization reaction is first described. This transformation enables the formation of new C(sp3)−N and C(sp2)−N bonds via the selection of different oxidation conditions. The features of this method include tunable product selectivity, excellent chemoselectivity, readily available starting materials, broad substrate scope, good tolerance of functional groups, and moderate to high yields. [ABSTRACT FROM AUTHOR]

A novel and efficient technique has been designed for the creation of oxygen vacancies on La2Ti2O7 (LTO) nanosheets. This is achieved via a controlled solid-state reaction between NaBH4 and LTO nanosheets. Transmission electron microscopy (TEM) analyses expose that these processed LTO specimens possess a unique crystalline core/amorphous shell structure, represented as La2Ti2O7@La2Ti2O7-x. According to X-ray photoelectron spectroscopy (XPS) observations, there is a notable correlation between the reaction time, temperature, and the concentration of oxygen vacancies. The concentration of these vacancies tends to increase along with the reaction time and temperature. Concurrently, UV-Visible spectra and photocatalytic tests reveal a significant impact of oxygen vacancies on the LTO surface on both light absorption and photocatalytic functionality. Most notably, the LTO nanosheets with engineered oxygen vacancies have demonstrated an exceptional photocatalytic capacity for hydrogen production under visible light. The maximal activity recorded was an impressive 149 μmol g−1 h−1, which is noticeably superior to the performance of the pristine La2Ti2O7. [ABSTRACT FROM AUTHOR]

A silver‐catalyzed protocol for the synthesis of 3‐(1H‐isochromen)‐chromones is described. The method involves an initial 6‐endo‐dig cyclization of o‐alkynylbenzaldehydes and domino C−H alkylation and chromone annulation of the o‐hydroxyarylenaminones, which enables the installation of 1H‐isochromen and chromone in a single structure. This synthetic strategy is advantageous for the excellent regioselectivity, step economy, concise one‐pot methodology, gram‐scale synthesis, as well as high bond‐forming efficiency. [ABSTRACT FROM AUTHOR]

The utilization of vortex generators (VGs) within minichannels to enhance heat transfer finds widespread application in heat exchanger systems. Nevertheless, the existing literature concerning VG employment remains positioned along a single wall surface of the channel. Within the scope of this investigation, perforated rectangular winglet VGs affixed to the relative wall are adopted, exploring four punching indexes (PI = 0.05, 0.10, 0.20, and 0.40) alongside three pitches (15 mm, 30 mm, and 45 mm). Across Reynolds number (Re) spanning from 2500 to 3500, a combined methodology involving numerical and experimental analyses is employed to quantify parameters such as Nu / Nu 0 , f / f 0 , and TEF , thereby assessing the impact of hole and pitch parameters on flow and heat transfer. Additionally, the examination of vortice structures is conducted using the Q method and secondary vortex intensity. The findings suggest that diverse VG hole parameters primarily influence the topological structure and intensity of downstream mixed vortices. With increasing PI values, the pronounced augmentation of jet flow significantly mitigates the intensity of other mixed vortices, consequently diminishing overall heat transfer and pressure losses. Furthermore, validation of the results is carried out using the field synergy principle. [ABSTRACT FROM AUTHOR]

In coherent radiation of an ensemble of electrons, the radiation field from electrons resonantly drives the other electrons inside to produce stimulated emission. The radiation reaction force on the electrons accounting for this stimulated radiation loss is classically described by the Liénard-Wiechert potential. Despite its being the foundation of beam physics for decades, we show that using the "acceleration field" in Liénard-Wiechert potential to describe radiative interactions leads to divergences due to its implicit dependence on instantaneous interactions. Here, we propose an alternative theory for electromagnetic radiation by decomposing the interactions into an instantaneous part and retarded part. It is shown that only the retarded part contributes to the irreversible radiation loss and the instantaneous part describes the space charge related effects. We further apply this theory to study the coherent synchrotron radiation energy loss, which hopefully will reshape our understanding of coherent radiation and collective interactions.