Both the intrinsic anisotropic optical materials and fullerene-assembled 2D materials have attracted a lot of interests in fundamental science and potential applications. The synthesis of a monolayer ...(ML) fullerene makes the combination of these two features plausible. In this work, using first-principles calculations, we systematically study the electronic structure, optical properties of quasi-hexagonal phase (qHP) ML and quasi-tetragonal phase (qTP) ML fullerenes. The calculations of qHP ML show that it is a semi-conductor with small anisotropic optical absorption, which agrees with the recent experimental measurements. However, the results for qTP ML reveal that it is a semimetal with highly in-plane anisotropic absorption. The dichroic ratio, namely the absorption ratio of \(x\)- and \(y\)-polarized light $\alpha$$_x$$_x\(/\)\alpha$$_y$$_y\(, is around 12 at photon energy of 0.29 eV. This anisotropy is much more pronounced when the photon energy is between 0.7 and 1.4 eV, where \)\alpha$$_x$$_x\( becomes nearly zero while \)\alpha$$_y$$_y$ is more than two orders of magnitude larger. This indicates qTP ML as a candidate for long-pursuit lossless metal and a potential material for atomically thin polarizer. We hope this will stimulate further experimental efforts in the study of qTP ML and other fullerene-assembled 2D materials.
High-performance computing, together with a neural network model trained from data generated with first-principles methods, has greatly boosted applications of \textit{ab initio} molecular dynamics ...in terms of spatial and temporal scales on modern supercomputers. Previous state-of-the-art can achieve \(1-2\) nanoseconds molecular dynamics simulation per day for 100-million atoms on the entire Summit supercomputer. In this paper, we have significantly reduced the memory footprint and computational time by a comprehensive approach with both algorithmic and system innovations. The neural network model is compressed by model tabulation, kernel fusion, and redundancy removal. Then optimizations such as acceleration of customized kernel, tabulation of activation function, MPI+OpenMP parallelization are implemented on GPU and ARM architectures. Testing results of the copper system show that the optimized code can scale up to the entire machine of both Fugaku and Summit, and the corresponding system size can be extended by a factor of \(134\) to an unprecedented \(17\) billion atoms. The strong scaling of a \(13.5\)-million atom copper system shows that the time-to-solution can be 7 times faster, reaching \(11.2\) nanoseconds per day. This work opens the door for unprecedentedly large-scale molecular dynamics simulations based on {\it ab initio} accuracy and can be potentially utilized in studying more realistic applications such as mechanical properties of metals, semiconductor devices, batteries, etc. The optimization techniques detailed in this paper also provide insight for relevant high-performance computing applications.
An intrinsic antiferromagnetic topological insulator \(\mathrm{MnBi_2Te_4}\) can be realized by intercalating Mn-Te bilayer chain in a topological insulator, \(\mathrm{Bi_2Te_3}\). ...\(\mathrm{MnBi_2Te_4}\) provides not only a stable platform to demonstrate exotic physical phenomena, but also easy tunability of the physical properties. For example, inserting more \(\mathrm{Bi_2Te_3}\) layers in between two adjacent \(\mathrm{MnBi_2Te_4}\) weakens the interlayer magnetic interactions between the \(\mathrm{MnBi_2Te_4}\) layers. Here we present the first observations on the inter- and intra-layer phonon modes of \(\mathrm{MnBi_{2n}Te_{3n+1}}\) (n=1,2,3,4) using cryogenic low-frequency Raman spectroscopy. We experimentally and theoretically distinguish the Raman vibrational modes using various polarization configurations. The two peaks at 66 cm\(^{-1}\) and 112 cm\(^{-1}\) show an abnormal perturbation in the Raman linewidths below the magnetic transition temperature due to spin-phonon coupling. In \(\mathrm{MnBi_4Te_7}\), the \(\mathrm{Bi_2Te_3}\) layers induce Davydov splitting of the A\(_{1g}\) mode around 137 cm\(^{-1}\) at 5 K. Using the linear chain model, we estimate the out-of-plane interlayer force constant to be \((3.98 \pm 0.14) \times 10^{19}\) N/m\(^3\) at 5 K, three times weaker than that of \(\mathrm{Bi_2Te_3}\). Our work discovers the dynamics of phonon modes of the \(\mathrm{MnBi_2Te_4}\) and the effect of the additional \(\mathrm{Bi_2Te_3}\) layers, providing the first-principles guidance to tailor the physical properties of layered heterostructures.
Pedestrian re-identification (Re-ID) via cross-camera is a difficult problem in the field of pedestrian discovery and tracking. Traditional solutions rely heavily on the external characteristics of a ...pedestrian's appearance. Maximally Stable Color Regions (MSCR), RGB (Red, Green, and Blue), HSV (Hue, Saturation and Value), and Histogram of Oriented Gradient (HOG) are usually used features. However, a single feature often cannot get a good matching result Multi-feature fusion has become a preferred method. This approach often requires determining the proportion of various features in the fusion process. In this paper, a method is proposed and used to confirm the proportion of various features at the optimal matching rate. The experiments are operated on a well-known dataset. Finally, the best weight combination of MSCR, RGB, wHSV, and HOG was determined by the proposed method.
More and more office buildings are built and consequently, the building energy-consumption increases especially air conditioning energy consumption. The energy consumption of air conditioning is ...monitored in an office building in Qingdao, and the test results show that refrigerator installed capacity is too large and COP is low, cooling circle pumps and chilled water pumps are oversize and water transport factor is lower than the standard value, the efficiency of the cooling tower is also very low. Based on experimental result, corresponding energy saving measures are proposed.
Based on energy storage balance of soil, the ideas to solve cold / heat stacking problem of the ground-source heat pump(GSHP system were put forward, further concepts of short intermittent operation ...and long intermittent operation were introduced. The soil temperature recovery of GSHP system with intensive vertical pipe was tested in a residence community during the transition season, relative operation strategy was discussed.
