Large-eddy simulation and control of flow separation over Ahmed car model

To be completed later</p

Solidification microstructure and tensile deformation mechanisms of selective electron beam melted Ni3Al-based alloy at room and elevated temperatures

Selective electron beam melting (SEBM) was used to process crack-free Ni3Al-based IC21 alloy (low density superalloy) containing ~85% γ′-volume fraction. There are distinct differences between dendrites and inter-dendritic regions with the presence of coarse γ+γ′ eutectic and secondary solidification microconstituents (Cr and Mo-rich) in the latter. The pronounced inter-dendritic eutectic regions suggest that a significant elemental partitioning between the liquid and solid occurred during the SEBM. The terminal liquid is trapped at boundaries between dendrites and grains, as evidenced by the liquid films on cracked surfaces. In contrast to extensive studies indicating the segregation of Zr and B, we show unambiguously the segregation of Si to low melting point liquid films and thereby enhancing the susceptibility to solidification cracking in IC21 produced by SEBM. The tensile specimens extracted from the crack-free IC21 samples exhibit superior properties at room temperature (RT) and 1000 °C. The RT deformation mechanism is characterised by cutting γ′-phase with two paired dislocations and antiphase boundaries in between. At 1000 °C tensile deformation, the well-developed γ/γ′ interfacial dislocation networks are in good agreement with their promising high-temperature performance (σ = 518 ± 10 MPa, σ = 560 ± 16 MPa, 20.5% for ductility)

Deep Hybrid Neural Network-Based Channel Equalization in Visible Light Communication

In this letter, the channel impairments compensation of visible light communication is formulated as a time sequence with memory prediction. Then we propose efficient nonlinear post equalization, using a combined long-short term memory (LSTM) and deep neural network (DNN), to learn the complicated channel characteristics and recover the original transmitted signal. We leverage the long-term memory parameters of LSTM to represent the sequence causality within the memory channel and refine the results by DNN to improve the reconstruction accuracy. Results demonstrate that the proposed scheme can robustly address the overall channel impairments and accurately recover the original transmitted signal with fairly fast convergence speed. Besides, it can achieve better balance between performance and complexity than that of the conventional competitive approaches, which demonstrates the potential and validity of the proposed methodology for channel equalization.</p

A very luminous jet from the disruption of a star by a massive black hole

Tidal disruption events (TDEs) are bursts of electromagnetic energy that are released when supermassive black holes at the centres of galaxies violently disrupt a star that passes too close1. TDEs provide a window through which to study accretion onto supermassive black holes; in some rare cases, this accretion leads to launching of a relativistic jet2–9, but the necessary conditions are not fully understood. The best-studied jetted TDE so far is Swift J1644+57, which was discovered in γ-rays, but was too obscured by dust to be seen at optical wavelengths. Here we report the optical detection of AT2022cmc, a rapidly fading source at cosmological distance (redshift z = 1.19325) the unique light curve of which transitioned into a luminous plateau within days. Observations of a bright counterpart at other wavelengths, including X-ray, submillimetre and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron ‘afterglow’, probably launched by a supermassive black hole with spin greater than approximately 0.3. Using four years of Zwicky Transient Facility10 survey data, we calculate a rate of 0.02−0.01+0.04 per gigapascals cubed per year for on-axis jetted TDEs on the basis of the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X-ray and radio observations11. Correcting for the beaming angle effects, this rate confirms that approximately 1 per cent of TDEs have relativistic jets. Optical surveys can use AT2022cmc as a prototype to unveil a population of jetted TDEs